Testosterone is my favourite hormone, a focus of my research. In the public mind it is the body most potent chemical, making the diference between a 90-pound weakling and a he-man, between a milquetoast and a lothario. Steroid analogues, stacked by muscle builders, are supposed to cause out-of-control “’roid rages�. Some people - lieve an injection of testosterone propelled Floyd Landis from also-ran to his “mirac- lous Stage 17� of the Tour de France. The hormone has become part of the language of popular cultureT . he New York Times carried the following passages in the previous 2 weeks: “I always thought downtown had a high testosterone level�, referring to the high ma- to-female ratio of residents in lower Manhattan (14 April 2007). “It is the kind of gathering that, at its most primal, has testosterone fowing more freely than the on-the-house spirits�, referring to a news conference prior to a boxing match (20 April 2007). “[T]hese are testosterone-fueled domains, largely defnedby bulging muscles and e- ploding guns�, in a review of an action movie (20 April 2007). “[T]his flm is about [auto racing] surfaces, for young men with testosterone to burn�, from a review of another action movie (14 April 2007).