The disease is Slow-Payitis. The victims are doctors, dentists and psychiatrists.

Medical professionals have particularly strong problems collecting their bills, according to Leonard Sklar, president of Medicon, co-sponsor (with local credit agencies) of seminars in collection techniques across the country.

"There's a reluctance on the part of doctors to discuss their fees with patients," says Sklar. "Doctors are thrown out into the world of business and have no education in this area. And, as their fees go higher, the patients' resistance mounts accordingly."

Sklar, 45, formerly an economist with IBM, founded Medicon in 1970. Its seminars specialized originally in teaching collection techniques solely to the medical professions, but the San Francisco-based corporation has expanded recently into other professional areas, with an emphasis on the insurance industry. There are currently 10 Medicon seminar leaders teaching collection techniques in 70 cities.

Fifty-five physicians' and dentists' assistants (along with this writer) paid $35 each for a recent half-day seminar co-sponsored by Medicon and Credit Research Co. Inc. at Tyson's Corner Ramada Inn.

"You'll notice," said Medicon seminar leader Fred Chafin as an opener, "that we got your money before you came in . . . unlike the way most of you do business for your doctors and dentists." The audience, mainly women, giggled nervously at the admonishment.

In dealing with the majority of patients who are honest and who want to pay their bills, Chafin counsels a straightforward approach. "The most important rule in dealing with patients is to be human and to tell the truth."

Payment, he said, should be discussed with the patient at the initial office consultation, preferably using a written financial policy.

"You don't like to ask for money because you think it isn't professional," he said. "But really it's because you're scared to do it. You don't want to confront them.

"Look at your local Safeway. If you don't have the money, you can't get groceries. Grocery stores have changed from Mom-and-Pop stores which would give you credit. Why haven't doctors changed?"

In pursuit of that end, changing doctors' (and their assistants') views about collecting fees, various techniques -- some less-than-gentle -- were presented at the seminar. (If you're a reluctant billpayer, you might someday find yourself on the receiving end of the approach.)

To demonstrate what an assistant should do when a patient is evasive about payment, Chafin asked for a volunteer to help him role-play an office confrontation. A woman agreed to be Ms. Jones, who had forgotten her checkbook and could not pay her $40 bill.

The woman rose from her chair. "I'm sorry," she told Chafin, "but I have only $20 in cash and I have to use that to buy the prescription. I just forgot because I was in such a rush."

"That's okay," replied Chafin. "I'll take your $20 in cash and I'll give you an envelope to send the rest to me. I'll mark my calendar that this will be in the mail today, Friday, so that I'll receive it by Monday."

The woman sat down. "I'd never be able to stand up to that," she said.

Hands went up. Everyone, it seemed, wanted to know when they should use stamped envelopes.

"Only with geriatric patients," said Chafin. "And when you do that, go to the post office and buy a book of commemorative stamps. There's a psychological thing about those stamps. People will hold onto them and value them and use the envelope.

"And it's very important to write down the date that you expect payment. Write this down in front of the patient. And get a big calendar to do this on -- or at least a medium-sized one. This will make an impression on the patient."

Problems multiply, said Chafin, once the patient is out of the office without paying his bill.

"If you have a debtor who's sending you $5 a month, then he could probably send you $10. It's just more convenient to send $5. So, take a red marking pen and make parallel lines across the check. Within these lines, write 'rejected.' And accompany this with a letter demanding payment within 48 hours."

Telephone calls are often more effective than letters, Chafin advises, in spurring debtors to pay their bills.

"Always request the entire balance two or three times during the conversation," he said.

"This establishes a basis of negotiation, and a greater probability that you'll get more money. And don't ever say that you know there's a good reason why they haven't paid their bill. Everyone has his excuses -- a trip to the Bahamas, a new car, a new house, whatever.

"Just stick to the point: the bill. Use the broken-record technique. Just keep repeating that the debtor owes the bill."

If a debtor turns truculent, Chafin advises a counterattack.

"Take a debtor who complains about being called at 7 a.m. Talk back. Say, what about me? I had to get up at 6 a.m. to call you first thing this morning. And if they complain of harassment, counterattack again. What do you mean, harassment? I've sent you five letters, three final notices, and I'm harassing you? Ha."

How successful are the collection techniques taught at Medicon seminars? Medicon president Sklar reports that there has been "no systematic feedback" from participants.

"Essentially, our seminars give people the courage to do what they want to do anyway," he said."People who do business want to be paid, but they're afraid to ask for money for fear of endangering their business. Some of them stay incompetent, in spite of the seminars. Others put our ideas into effect."

Adds Darlene Dauphin, Medicon's director of credit services: "Information persists that as long as someone is making an effort to pay, you cannot ask for full payment, but this isn't so. Whatever works within the frame of the law and the frame of ethics is a reasonable technique . . .

"You may be talking about a year or two passing without a response . . . The doctor has a patient load, and there may be 200 people who are failing to pay him, so that he won't be able to pay his bills either."

As the seminar at Tyson's Corner ended, the participants left the room slowly, gathering up notes and materials, comparing names and specialties of their bosses. Some complained of people with diamonds on their fingers who refuse to pay their bills. Others murmured that they would be fired if they used the abrasive techniques they had just been taught.

A woman commented that getting payment is "just a matter of confidence, that's all. It comes across in your voice."

One woman listened to another's account of working for a young, inexperienced doctor who is afraid to ask his patients for money. She shook her head. "If he's that young, he's probably still idealistic. He'll learn."