Deep in the forests of northern Thailand, far from the pounding noise of Bangkok's streets, a leaf crunched underfoot as we crested a hill. We were near the famous "Golden Triangle" opium-producing region, among 50-foot trees and waist-high grass. We followed the narrow trail around a bend.

There in the valley below, a hill-tribe village of about 35 straw huts slept in the late-afternoon sun. Smoke rose gently from cook-fires; a child fetched water from the slow-moving stream that wound its way around the village.

Our group of 10 trekkers followed our guide to the hut where we would sleep. Chickens clucked, pigs waddled through the village, and dogs outside each house barked warnings. Two women in brightly patterned clothing stepped on and off a seesawlike pestle to pound rice. A third woman tossed the smashed rice into the air, letting the wind blow away the chaff. Another group performed the same chore 10 yards away.

This village, like most of the five camps visited on our four-day trek, appeared to be basically a primitive culture with few trappings of modernity. The prehistoric life style of the hill tribes is so easy to see that treks to hill-tribe villages have become one of the hottest tourist industries in Chiang Mai, Thailand's second largest city. Two-day, three-day, four-day, even eight-day treks are offered to a variety of villages of the Akha, Lisu, Lahu, Yao, Karen and Meo tribes. (One-afternoon visits by motorbus are also available, but hardly qualify as a trek.)

The big question is whether you want to include elephant-riding. Three-hour elephant rides and all-day raft trips are available as options on some treks. But scuttlebutt had it that all the "elephant treks" went to areas that had seen many tourists (hill-tribe trekkers put a great premium on the relative virginity of their villages), so I settled for a simple four-day walk. Except for the final village, the route had seen no more than four or five sets of tourists, our guide swore.

The walk itself was the highlight of the trip for some of the trekkers. Even if teak trees were few, we had marvelous glimpses of hillsides and meadows and jagged peaks. We passed fields of tobacco and corn, and of stumps of hardwood trees. Hunting parties set out with eight-foot rifles to shoot fowl. Water-buffalo-driven carts slowly carried hardwood boards along dirt roads. In one grassy meadow two men sawed a huge block of hardwood -- one man stood on top of the block and one underneath.

Though the Thai government is trying to stamp out the crop, our guide led us on a detour to a field of opium poppies. White and red flowers waved in the breeze. Other bulbs showed scars where they had been slit to remove the oozy serum. Two tribal women tended the crop: A teen-ager in a bright pink blouse examined the flowers; an elderly woman with bright red betel nut-stained lips stuck tiny holes in the stems.

Gentle tribes people like these are the beginning of the chain that ends in heroin in western veins. The Thai government is trying to integrate the tribes into national life and wean them to other sources of income; it was during these attempts that the tribes' appeal to tourists was discovered.

For me, the highlight of the trip was the chance to observe village life -- people living something like our ancestors must have lived 4,000 years ago. Many tribes people kept a discrete distance, but others -- especially the children -- stared constantly. In one village in a valley, a group of children watched us eat dinner; I taught them to sing "Nice-to-meet-you" in a simple four-note progression. Several hours later, cherubic voices could be heard around campfires, singing "Nice-to-me-chyoo."

Women in one village offered to sell us bracelets. But in the valley village, one trekker saw a gourd she wanted to purchase, and a price of 10 bahts (40 cents) was set; when the seller went to check with the village headman, he returned to say the gourd was not for sale -- at any price. "He says they need the gourd more than they need money," our guide explained. A retired Los Angeles couple, who have circled the world, had a similar experience on their trek: "In one village they said they had an extra shirt," recounted the woman. "Did Alex want a shirt? Well, yes, but the shirt was too small. Could he have a larger shirt? No, they explained, this was the extra shirt. There was not another unneeded shirt in the village."

One night, as we sat in near darkness in our hut, a hill-tribe man smoked opium in a sensuous ceremony. He brought in a gas lamp for light and a small, circular oil candle to warm the dope. As he lay down, he placed a small, shiny silver circle around the oil candle's tiny flame. He used a delicately curved, thin silver stick with a fine point to bring the opium near the flame; then he shaped the drug into a ball on the stick's point. He placed the opium around a tiny hole in a huge bamboo pipe and lit it. As he inhaled, he used the stick to push the bubbling opium into the hole.

After several pipefuls, his eyes were slits, and he seemed to be shaping the opium onto the silver stick by feel rather than sight. But when a tribal child got too close to his gas lamp, he jumped to his feet with catlike agility.

At another village, we were offered opium for sale. Some treks that actually enter the "Golden Triangle" reportedly draw a fair proportion of people attracted mainly by the chance to smoke opium, but no one in my group, as far as I know, tried it.

We all felt guilty about taking pictures of tribes people, although take pictures we all did. We felt most guilty at our first village, when our guide paid some villagers to put on a dance-and-music show for us. The rest of the villagers stared, entranced. We were witnessing the Dawn of a Tourist Industry; visions of "Traditional Dances Performed Nightly" 10 years hence went through my mind. Then the guide had us do a Western song for the villagers. We sang "Kookaburra" in a round to great applause.

Interaction with the tribes was less than we might have liked, partly because we were fatigued by the time we reached each village, partly because our guide did not do much translating. We smiled, pointed and hand-signaled. Mostly, though, we simply observed hill-tribe life, and greatly enjoyed that.

We also left presents. One trekker gave a cigarette lighter "for starting cook-fires." Another gave Band-Aids and disinfectant. Someone else introduced one village to western cosmetics. Adults and children alike sported white faces from Johnson's Baby Powder.

Everybody on my trek -- even those who brought summer-weight sleeping bags -- complained about the night cold, which the paper-thin blankets most tour companies provide do little to keep out.

Our trek had some organizational problems, including a six-kilometer backtrack -- while we hikers were wearing thongs -- and poor timing that found us, at one point, walking for four hours up and down hills with packs during the hottest part of the day.

Interviews with other trekkers in Chiang Mai indicate that these -- with the exception of the six-kilometer thong hike -- are common problems.

But the blisters, the sweating and freezing all became worthwhile on our last day, when we saw what we had been missing. Our final stop was a Meo village that sat smack dab next to the highway. The differences were apparent from the moment we walked in. On the far side of the village were souvenir stands.

In retrospect, I suspect "our" villages had seen more than the four or five sets of trekkers our guide mentioned. Women in one of the villages, for example, refused to have their pictures taken -- but people in less materially developed cultures usually love cameras until they've been photographed too much. Our reception was somewhere between the energetic curiosity that meets the first visitors to a village and the easy hucksterism that marks a society grown accustomed to wealthy foreigners. Our villagers were in the in-between stage -- much of the time they ignored us and just went ahead with their lives.

And that is exactly what I wanted.

Brooks Roberts Fudenberg, a Washington writer, is currently traveling around the world.