It goes by many names. "Male menopause" is perhaps the most popular, but "andropause" is the term that many doctors favor, and PADAM ("partial androgen deficiency in aging men") has its partisans, too. The condition may afflict millions of Americans, and, if they do not yet recognize the symptoms, a public-awareness campaign has been launched to help them. A two-page ad that ran in Time not long ago showed a car's gas gauge pointing to Empty and beside it the words "Fatigued? Depressed mood? Low sex drive? Could be your testosterone is running on empty." The ad explains that "as some men grow older, their testosterone levels decline," and that such men should consult their doctors about testosterone therapy. At the bottom of the page, the gas gauge points to Full.

Physicians have been targeted with similar ads. One that appeared in a recent issue of a primary-care journal calls on them to "identify the men in your practice with low testosterone who may benefit from clinical performance in a packet." The photographs are eye-catching: there's a well-built fellow in his middle years beside the words "improved sexual function"; a smiling man in shorts and a T-shirt who is standing next to a mountain bike ("improved mood"); a policeman directing traffic ("increased bone mineral density"). Doctors are told to "screen for symptoms of low testosterone" and "restore normal testosterone levels."

These ads were paid for by Unimed, a division of the Belgian conglomerate Solvay. Unimed makes AndroGel, a drug that was approved by the F.D.A. two years ago, and is the fastest-growing form of testosterone-replacement therapy for men. Pills, introduced in the sixties, often caused liver damage. Intramuscular injections, particularly favored by bodybuilders and competitive athletes, produce a sharp spike of the hormone, and then a fall, and these fluctuations are often accompanied by swings in mood, libido, and energy. In the late eighties, a transdermal patch was developed, and its use is still widespread. The patch provides safer and steadier dosing, but often causes skin irritation, and sometimes falls off during exercise. AndroGel, by contrast, delivers testosterone in a colorless, drying gel that is simply rubbed on an area of the body-usually the shoulders-once a day. It has thus made testosterone available in a form that almost any man can use conveniently.