Whether the causes are (1) psychological or (2) physical, says Pfizer Pharmaceuticals, one's chances of arousal are 81% in the first group and 59% percent in the second. It is estimated that as many as 30 million American males suffer varying degrees of erectile dysfunction.

The arrival of this oral medication has only one major drawback, namely that it eliminates a certain degree of spontaneity. A user must determine beforehand in the day that he'll be enjoying sexual relations later.

Some testees experience, as side effects, nausea, headaches and flushes. Men taking nitroglycerin must forego taking the new drug.

Previous medical responses to impotence have included an injection into the penis, vacuum pumps, surgical implants and pellets. These alternatives, less than encouraging, may now go the way of the dodo. Viagra is the first medical stimulant that can be taken orally. Men are expected to prefer it to all previous treatments.

As such, say its enthusiastic promoters, it stands to become one of the top-selling drugs of all time.

A man must be sexually aroused, say FDA spokesman, in order for the drug to take effect. Instead of working mechanically, as did previous methods, Viagra mimics the natural routes to arousal.

Urologists believe that the most significant aspect of Viagra's arrival is that it will put erectile dysfunction on the radar screen for both patients and their partners.

Persons with undetected diseases that cause impotence—such as diabetes or petuitary cancer—may go into doctors' offices earlier than they might otherwise do, hoping for a viable treatment for their erectile problems.

The cost of Viagra is $7 per pill. Its generic name is sildenafil.

Whether the physical problems causing impotence are spinal cord injuries, prostate surgery, or diabetes, Viagra has been found helpful.

By the year 2001, the erection drug is expected to bring its makers as much as $2 billion, say market analysts. In the future, annual sales could rise to $5 billion.