Nocturnal penile tumescence and serum testosterone levels.

Ten patients with chronic epilepsy were selected; five had high and five had low total serum testosterone levels. Each patient slept for two nights in the sleep laboratory. EEG monitoring and measurements of nocturnal penile tumescence were carried out during sleep. A clear relationship between both total and free serum testosterone levels were found with nocturnal penile tumescence. FSH, LH, SHBG, and prolactin showed no relationship. The five patients with low serum testosterone levels all showed reduced sexual activity.