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We agree that our description of the impact of testosterone on penile erections1 was unclear. The literature supports a modulating role of testosterone on erectile function.2 This hormone clearly increases responsiveness to phosphodiesterase type 5 inhibitors, and testosterone levels correlate with measured frequency of sleep erections. However, testosterone levels do not directly correlate with erectile function, and supplementing low levels of testosterone in hypogonadal men or administering exogenous testosterone to eugonadal men generally does not enhance erectile performance.
Gerald Brock Division of Urology Faculty of Medicine and Dentistry University of Western Ontario London, Ont.