Previous endocrine investigations have demonstrated the presence of multiple impairments of pituitary-target gland function in heroin addicts suggesting a possible hypothalamic involvement. Since the response of the pituitary to nonspecific stimuli is considered an expression of hypothalamic dysfunction, indicating a disconnection between the central nervous system and the anterior pituitary, we thought it worthwhile to study the GH response to stimulation with thyrotropin-releasing hormone (TRH) or gonadotropin-releasing hormone (GnRH) in heroin addicts. 23 male heroin addicts, aged 18-40 years, with histories of addiction to heroin alone from 8 months to 4 years, and daily i.v. heroin intakes between 200 and 2,500 mg of the drug (containing 18% of pure heroin) were studied. 8 patients received TRH 500 µg, GnRH 150 µg and 5 saline only, intravenously, and GH levels were assayed radioimmunologically in bloods taken 3Omin before, at the moment of stimulation and 15, 30, 60, 90 and 120 min thereafter. The results show normal basal GH levels. Stimulation with TRH and GnRH induced marked GH hypersecretion in 8 of the 18 patients examined. These results suggest that the hypothalamopituitary function may be impaired in heroin addictio