To test the effect of methadone on hormone release in man, plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17-beta-estradiol (E2), estrone (E1), progesterone (P), testosterone (T), dehydrotestosterone (DHT), androstenedione (A), dehydroepiandrosterone sulphate (DS), and prolactin (PRL) have been evaluated in 25 male subjects in treatment wit 30 mg/day methadone per os for at least two months after a minimum of one year of heroin addiction. All subjects had a history of sexual difficulties. The levels of E1, E2, P and LH were always within normal values whereas FSH showed lower values than normal and A, DS and PRL noticeably increased in many subjects. Modest variations were noted for T and DHT. These data seem to indicate that methadone abuse affects the hypophysis, the testiculum and the adrenal cortex. More details will probably be obtained when the variations in hormone rates and opiate serum concentrations are checked at a later date.