Though the chronic use of opiates can modify several body functions, only a few data are available on the effects of opioid drugs on mineral metabolism. We have examined the possible consequences of chronic opiate abuse on bone mass, bone turnover and calcium metabolism in 13 male chronic heroin users, examined 1-2 days after the last administration of the drug (group A), 14 former male heroin addicts, examined 4-24 months after drug discontinuation (group B), and 22 healthy, age- and sex-matched control subjects. In group A, the vertebral bone mineral density (measured by Dual-Photon Absorptiometry) was significantly lower (p < 0.05) than in the control subjects, despite similar values of total body bone mineral, lean body and fat mass. Blood-ionised calcium and urinary calcium and hydroxyproline were significantly increased (p < 0.01), whereas parathyroid hormone was lower than in controls (p < 0.01). Bone alkaline phosphatase and osteocalcin, however, were not significantly different from the control values. LH and testosterone levels were low (p < 0.01 vs controls). In contrast, group B subjects did not show significant differences from the control group. The chronic abuse of opioid drugs may be associated with altered bone metabolism and reduced trabecular bone mass, attributable, at least in part, to gonadal deficiency. These alterations seem reversible after drug discontinuation.