We report here the results of a survey of 308 intravenous drug abusers recruited from hospital-based methadone maintenance or drug detoxification programmes located in Manhattan, New York City. Complete interviews and serological analyses for antibodies to human immunodeficiency virus (HIV) using both enzyme-linked immunosorbent and Western blot assays were obtained from 290 (94%) of the subjects. HIV antibodies were found by both assays in 147 (50.7%) of the tested subjects; conflicting results were found in three (1%) of the subjects; and negative results on both tests were found in 140 (48.3%) of the subjects. Logistic regression analysis identified significant relative risks for HIV infection associated with the frequency of drug injection and the proportion of injections in 'shooting galleries'. Additional risk among men was associated with a history of homosexual relations. Traditional efforts taken by subjects to clean syringes between uses, such as washing with water or alcohol, showed no evidence of being protective. Programmes aimed at prevention of HIV infection should focus on reducing use of shooting galleries and sharing of needles and syringes as well as reducing intravenous drug abuse generally.