Since 1966, when an Egyptian surgeon first pioneered the use of penile implants, the devices have grown in popularity. Estimates are that 20,000 to 30,000 such operations are performed each year in the United States, says Dr. David McLeod, chief of urology at the Walter Reed Army Medical Center, where some 600 devices have been implanted since 1978.

Three general types of implants are now on the market. One is semi-rigid, and maintains a partial or full erection. The other two rely on pumps to inflate the penis. All involve implanting devices in the corpora cavanosas -- literally dilatable spaces within the penis which fill with blood during an erection. In the impotent man, the penile implants perform this function.

Few people question the use of penile implants for men who are permanently disabled -- those with multiple sclerosis, paralysis, spinal cord injuries, or severe forms of diabetes that have irreversibly damaged blood vessels.

"I think it's a really fine thing to do in many of these cases," says Dr. Patricia Schreiner-Engel, a psychologist and director of human sexuality at New York's Mount Sinai Hospital.

But when it comes to using the devices in men without clear physical impairment, some sex therapists express reservations.

"I think that one would have to recommend extreme caution to use a surgical solution such as the implant to a psychological problem," says Dr. R. Taylor Segraves, professor of psychiatry at Tulane University Medical Center in New Orleans.

One problem is that insertion of the implant requires permanent removal of penile tissue. "You can take the implant back out, but you have destroyed erectile tissue," Segraves says. "I don't see how a man could have an erection after that."

"I can see the concern on the sex therapists' part," says Walter Reed's McLeod, noting however, that "there is a large population out there who needs them. I think this has been a great thing for people. Impotence used to be the bane of our existence. Now we've got a way to treat it."

But patients must be carefully screened before having the surgery, McLeod cautions. "We are very conservative in choosing the people who get them."

Some sex therapists still worry, however, that the implants are being used too often, before men with psychological causes of impotence have a chance to work out their problems.

"It's very straightforward, easy surgery and a big money maker," says Schreiner-Engel. "It can be very easily abused. I keep hearing about younger and younger men having it done."

One recent case involved a 35-year-old man who became impotent after going bankrupt. "There was no organic process going on," Schreiner-Engel says. "Yet he was in surgery within a matter of days."

Another problem with the implants is the reaction of wives and partners. "Female partners are often horrified," says Schreiner-Engel. "They don't like the idea of implants ." As a result, studies suggest that some men never use their implants.

Says Segraves: "We really need to evaluate the data more on these implants."