What's more popular than all the Sheratons, Westins and Four Seasons in the world combined?

Your house.

Fact is, although the hotel industry pours billions of dollars into enticing travelers into for-hire lodgings, 48 percent of all leisure travelers last year stayed with friends or relatives, according to the Travel Industry Association of America. It's a figure that varies little from year to year, always hovering near the halfway mark.

Most of those millions of visits start like this: The phone rings. Someone on the other end says, "We'll be passing through, and wonder if we could drop by."

Everyone knows the caller isn't talking about a coffee break, but a self-invite for overnight accommodations, often of unspecified duration.

It's a question that sometimes makes the blood run cold, judging from the heartfelt responses of readers when we invited them to tell us about their experiences with hosting -- and being -- houseguests.

Oh, there were some delighted hosts and guests who wrote about how they treasure their home-based overnight encounters with friends, relatives and even strangers. Art Kosatka and Maureen O'Hara of Olney, for example, adore hosting Japanese students each year, even though they flinch at watching them eat pizza slathered with mayonnaise and topped with dried fish and cabbage.

Julie Puckett of Centreville loves to host her mother-in-law, who "pitches in whenever needed," "stops by the grocery store to replace food items she's used" and leaves the guest room "as clean, if not cleaner, than when she arrived." Ruth E. Thaler-Carter of Rochester, N.Y., marvels at the Washington friend who keeps a coffeemaker, with mugs and condiments, in the guest bathroom. Pat Tollifson of Shepherdstown, W.Va., loves and now emulates the friend who washes the sheets and remakes the beds before departing.

But the odes of joy that reached our mailboxes were far outnumbered by the still-raw memories of guests and hosts from the land of bad manners. Guests who not only invited themselves for long visits on short notice, but who brought other guests, too. Sandy towels clogging washing machines. Guests who ran up huge phone bills, or tried to change their hosts' religious or political beliefs. Empty-handed guests who not only expected a full breakfast and dinner, but packed themselves a lunch before heading out for the day.

Your popularity as a host, many readers told us, may have less to do with your stellar personality than with the amenities of the locale where you've chosen to live. Reader Debbie Gathercole, for example, found that friends and relatives were much closer spiritually when she lived far, far away -- in Maui -- than when she relocated much closer physically. In fact, friends and relatives who couldn't bear to be away from her for long when she lived in Maui for some reason don't miss her nearly as much now that she's tucked away in Winchester, Va.

Other readers raised issues we had never considered, like what to do if you find ticks in your host's bed, or a huge sausage beneath the keyboard cover of the grand piano.

With the help of etiquette specialist Letitia Baldrige, author of numerous books on manners and social secretary to the late Jacqueline Kennedy, we've created a primer both for those who are considering a drop-by, and for those who will be dropped upon.

Tips for Hosts

* Drop hints boldly. When an old college friend called Louanne Wheeler of Falls Church, saying she'd be in the area and would like to "stop by" with her husband and 4-year-old son that Tuesday, Wheeler agreed, even though it would be a trial to be a good hostess, given a new baby, a 4-year-old, a two-bedroom house and a husband on a business trip.

Wheeler subtly hinted that she wasn't expecting a long visit.

"It's too bad you won't get to see Art," she said, "since he won't be home until Friday."

The hint was too subtle.

"That's no problem," chirped the friend. "We have the whole week!"

Having found her doormat, the friend soon called back to let Wheeler know that she was also bringing along her friend Cindy, and Cindy's 4-year-old son. The friend then spent the week sightseeing with Cindy, leaving the husband and kids with Wheeler.

Let this be a warning: If your subtle hints blow by unnoticed, try being less subtle. If broad hints don't work, ask yourself if you're really prepared to expend a lot of hosting energy on dunderheads. If for some reason the answer remains yes, then pull out all the stops and get frank.

There is nothing wrong with telling guests in advance how long their welcome will last. Baldwin suggests a nice way of putting it. "They say, 'We're coming through town, can we stay with you?' You may answer, 'Of course we'll be thrilled to see you, but . . . ' " and then present the reasoning for why you can only have them one night, or two, or whatever your limit may be.

If it's a bad time, or the self-invited guests are not people with whom you want to share your home, you must . . .

* Just say no. Once you've agreed to be a host, obligations kick in. Whether you like it or not, those obligations remain as obligatory for self-invited guests you don't really like as they are for dear friends whom you've been begging to visit.

Expect to make breakfast and dinner, and don't expect help with the dishes. A good guest will of course offer, says Baldrige, but it's certainly not proper to ask for help, and accepting it stops short of true hospitality.

The host isn't required to squire visitors around town but must make it as easy as possible for the guests themselves to get around. That could mean anything from lending your car to providing bus schedules.

You secretly may be a reluctant host, but once you've accepted the job, you must not be a miserly one.

"If you are dumb enough to give hospitality to people you don't really like or trust or find attractive, you have to be ready to witness poor manners and bad behavior," says Baldrige. "You never have to throw a big party, but you are responsible for a guest's comfort and happiness. Otherwise, you should have said, 'Sorry, the house is being painted for the next three months.' "

* Beware of relatives. Relatives hold the potential for delivering a double whammy -- not only are they the hardest to say no to, but, unlike friends, they are the ones you don't get to choose in the first place. Little wonder that most horror stories were from readers hosting relatives.

Jane Brown of Burke took the relative-hosting business to its extreme by agreeing to take in her sister's British in-laws. She and her husband soon found they were expected not only to chauffeur the in-laws, but to pay for all incidentals, including out-of-home meals and admission fees to attractions. Worst of all: the harping about American ways, most particularly about lazy Americans and their aversion to walking.

Brown finally took revenge.

After a full day of sightseeing and repeated grousing about how Americans drive everywhere, she made one last stop and walked them through every corner of Arlington Cemetery -- every presidential grave site, the Tomb of the Unknowns, every building on the grounds. She heard no more grousing on the drive home: The Brits fell sound asleep in the back seat.

Baldrige points out another option: setting limits. "You must not make demands or be Gestapo-like, but it's perfectly acceptable to let the rules be known." You can give visitors a key, a public transport schedule, wish them a wonderful day, and say, "By the way, dinner is at 6:30, and the children will be eating with us."

Tips for Guests

* Report rotting sausages. It's been nearly 50 years since James and Grace Boeringer of Silver Spring honeymooned on Lake Erie, in the home of a minister who graciously offered the struggling young couple his home while he traveled abroad.

But every anniversary since the honeymoon, the couple has talked about whether they did the right thing:

On the last night, the couple decided to play a duet on the Steinway grand in the host's living room. They lifted the keyboard lid and found a sausage seeping fat and spices into the ebonies and ivories.

"Not a pale little Jimmy Dean breakfast sausage, but a thick and lumpy German sausage," writes James Boeringer. "A great fat link stretching from middle C to F, 21/2 octaves above."

What should they do? Move the sausage, play a few tunes, then replace it? Refrigerate the sausage and leave a note explaining the stains? Call to inquire as to the purpose of a keyboard sausage?

The Boeringers left the sausage and closed the lid, deciding to pretend they never saw it, should questions ever arise.

There indeed are times when you might not wish to question a host. For example, you should avoid saying something like, "Is it all right if I move the pornographic pictures of you and your husband out of the children's reach?"

But asking if a host would like a rotting sausage removed from his grand piano seems quite within the bounds of good taste.

In fact, Baldrige says that guests even have the right to awaken their guests to inquire about unusual or difficult circumstances. She says that Joan Tury of Annandale, for example, had no need to suffer in silence for five nights in a tick-ridden bed.

Tury said she "was taught that it is rude for a guest to complain. Cutting the visit short without a decent excuse seemed rude. [Saying] 'I can't sleep because you have ticks' didn't seem to cut it, either."

Of course you may never criticize a host's taste in decor or cuisine, or make smarmy remarks about the town where they've chosen to live. But you may, Baldrige advises, say, "I'm terribly sorry, but I'm so allergic to ticks. Would you mind if we went to a hotel for the night?"

In other words, never suffer in silence. You can even wake up a host and ask for pain medication and such, should it become necessary, says Baldrige. Given that, it's a good idea for hosts to set out common pharmaceutical necessities in a guest's room.

* Bear gifts. Guests would be amazed to read how much even a token gift means to their hosts. Or how put out they feel when a guest fails to show appreciation.

It's quite all right to delay giving a gift until immediately after returning home, the theory here being that you may have a better idea of what's needed in the household after your visit.

If you can afford to treat your hosts to dinner, that counts as a present. But even so, you must follow up with a note, says Baldrige, and preferably an additional little gift.

The longer you stay and the more people you bring, the more substantial the gift should be. If you can't afford more than, say, a box of stationery, send a beautiful letter. Sample text: "I wish I could send you a million orchids," says Baldrige. She adds, "Apologize for not giving a gift commensurate with your gratitude."

* Don't call the front desk. It's a common refrain: "They treated my home like a hotel." Each circumstance that elicits that cry is a bit different, but they all boil down to this: visitors who mistake their hosts for a professional staff that includes maids, cooks, waitresses, busboys and concierge.

Hosts are not maids, nor are they tour operators. They should be glad to make recommendations for places to visit and to eat, and even gather brochures. But "crack a guidebook before you arrive," says reader Ruth van Baak Griffioen of Williamsburg, who reports that of the 107 guests who visited her during her three years in the Netherlands, 104 were great.

She saw enough people coming and going to rack up a few pet peeves, though, including people who arrived without local currency or the proper tools to acquire some. Number one on her wish list: a guest who tells the host no later than on arrival when he or she plans to leave.

Seems reasonable: Even hotels ask for that.

While many readers complained about being mistaken for a hotel, Bill McCloskey stood out: His friend mistook his home for an RV park and grocery store.

McCloskey, of Bethesda, immediately opened his heart and driveway when an acquaintance he met through church contacts asked if his family could visit in their RV. He swallowed without comment when the guy hooked a fire-hose-size cord from the RV to McCloskey's electricity source. He watched while the family took food first by the loaf, then by the box, out of his house. Only when the guy's kids locked McCloskey's daughter out of the house was the RV family sent packing.

We didn't ask the etiquette expert about this one, but we think Baldrige would have approved.

* Don't overindulge. Donna Wiesner's guest mentioned on arrival that she'd be of no use around the house because she had a bad ankle.

Wiesner, of Alexandria, thought the guest might also be nearsighted, given how she'd sometimes walk in the opposite direction from an obvious destination.

She thought it a little odd when the woman's husband -- a friend of Wiesner's husband's -- had to grab her to keep her from falling down the stairs. But she does have that bad ankle, Wiesner thought.

The next morning, while both husbands were out fishing, Wiesner walked in to find the wife squatting on the floor in front of the liquor cabinet, a bottle upended in her mouth.

Every other bottle in the cabinet was just one shot shy of empty.

This takes us back to Baldrige's most basic advice: Host only those you know and love.

But given the problems, why get yourself entangled in the whole guest/host thing at all?

Because hosting, for all its potential pitfalls, is "one of the most loving, attractive things you can do for friends or family," says Baldrige. "It's a wonderful thing to do in this selfish world of ours."

And then, of course, there's the selfish perspective. Reciprocity, after all, is an assumed obligation of the guest/host relationship. You, the host, have earned an unspoken credit, good for one drop-by, while passing through.

For readers' tales on the joys -- and woes -- of houseguests, see Page P7.

Cindy Loose will be online to discuss this story Monday at 2 p.m. during the Travel section's regular weekly chat on www.washingtonpost.com.