Sexual behavior in connection with drug use and its implications for the risk of sexual transmission of human immunodeficiency virus (HIV) among intravenous drug users (IVDUs) was investigated in a pilot study of 29 men (who injected drugs more than once a week for at least 6 months) at the Remand Prison in Stockholm from November, 1989, to January, 1990. A structured interview focusing on sexual history and current sexual behavior with and without drugs was employed. The median age of the subjects was 32 years. Six were HIV-seropositive. The main drugs presently used were amphetamine (18 men), heroin (9 men) and cocaine (2 men). Of the 29 men, 27 had experience of sexual activity while using amphetamine. Of these, 23 reported that they became more sexually excited when on amphetamine, 21 reported intensified orgasms, and 23 reported that the drug prolonged intercourse. All 29 men had been sexually active, but only 6 of the amphetamine users had had more than 10 partners during the last 3 years. Condom use was very low; it was reported by only 3 men during their last intercourse with a causal partner. The findings suggest that sexual HIV transmission among IVDUs is a clear risk, especially among amphetamine users, and that education about condom use is urgent.