PROF. JAMES M. DABBS is to testosterone what Oliver Sacks is to madness. Champion. Iconoclast. Philosopher. Friend. "People want to characterize testosterone as having some powerful effect, often bad. It's sort of been scapegoated for all the ills in society," observed Dr. Dabbs, a social psychologist at Georgia State University in Atlanta. "But it's unfair to call testosterone unbrokenly bad."

Dr. Dabbs gives the maligned male sex hormone credit for generating a range of positive qualities, including confidence and a sense of well-being. "There is a lot of ignorance about testosterone," he said.

Testosterone is produced in the testicles and ovaries and, to a much smaller degree, in the adrenal glands. It is responsible for determining the biological differences between the sexes. Men have 8 to 10 times more than women do. Levels drop naturally as both sexes age. The amount in the blood varies from person to person, and from hour to hour; it is higher in the morning and lower at night. Extreme surpluses or deficiencies are rare.

Testosterone's bad reputation has been evolving since the early 1970's. Over the years "testosterone poisoning" has been blamed for everything from rape to low intelligence to road rage. A few notorious assault cases involving body builders taking huge amounts of anabolic steroids, a form of testosterone, have fueled the blame-the-testosterone effort.

However, research by Dr. Dabbs and other experts paints a more complicated and benevolent picture of this vital hormone. In 38 studies published over the last 12 years, Dr. Dabbs has reached the same conclusion: while it is true that testosterone affects behavior (and there is no question that it is the juice that fuels libido) there is no proof that it causes aggression.

On the other hand, certain behaviors can produce a testosterone surge. In a 1992 study of college chess players, Dr. Dabbs found that testosterone levels shot up in the victors and plunged in the losers after the matches were finished. This seems to indicate that hormone levels are a function of the outcome, not a cause of it. Similarly, Dr. Dabbs tested fans before and immediately after the 1994 World Cup soccer final between Italy and Brazil. In what Dr. Dabbs considers proof of the axiom "basking in reflected glory," testosterone levels swelled among the victorious Brazilians and sank among the dejected Italians. By extension, he predicts a baby boom this spring among the French, in tribute to their World Cup championship victory last summer.

DR. ALAN BOOTH, a testosterone expert at Penn State University, agrees with Dr. Dabbs that testosterone has undergone a stunning rehabilitation.

Dr. Booth notes that people are now less quick to demonize it as a social poison, and urologists are prescribing it more for men (and women) with low libidos without fear that it will have adverse effects on their moods or temperaments.

Even top endocrinologists like Dr. Andre Guay, the director of the Center for Sexual Function at the Lahey Clinic in Massachusetts, are arguing for a cultural pardon for testosterone. "What we thought we knew about testosterone in the past came from watching teen-age boys go into puberty and become obnoxious," Dr. Guay said. "But in the last few years, there has been an explosion in the testosterone world, a complete change in thought."

Researchers are now suggesting that the true abnormality may be testosterone deficiency rather than testosterone overload. A study published in the American Journal of Psychiatry last October found that extremely low levels of testosterone cause depression, anxiety, irritability, insomnia, weakness, diminished libido and poor memory.

"In fact, people with low testosterone levels are much angrier people," said Dr. Ronald S. Swerdloff, the chief of the endocrinology division at Harbor-U.C.L.A. Medical Center in Torrance, Calif. Dr. Swerdloff was among the first to experiment with testosterone replacement as a way to lift depression and defuse aggressive behavior.

Another long-held notion about testosterone that is getting a second look is the idea that high testosterone levels are linked to social dominance, the tendency of certain individuals to take command. It has long been assumed that people gain dominance by exhibiting aggressive behavior: being louder, more cunning or more physically menacing, for example. Dr. Dabbs disagrees. "Dominance need not be competitive," he wrote in a 1998 article in the journal Behavioral and Brain Sciences. "It can arise from strong personal characteristics that produce admiration and deference in others." Ordinary men and women may tend to award authority to people with leadership qualities, he argues, adding that, often, those people are their testosterone superiors.

Dr. Dabbs took photographs and studied the salivary testosterone levels of 114 women and 119 men, all local college students. He then showed the photographs, which were individual head shots, both smiling and unsmiling, to untrained volunteers and asked them to judge which people looked stronger and more dominant. Without fail, those chosen were the men and women with relatively high testosterone levels.

"There is something about interpersonal power and dynamism (or seriousness or substance or presence) that seems true among people with high testosterone," Dr. Dabbs said. "They are a little less concerned with what others are thinking about, a little more forward or bold or unafraid."