Between 1972 and 1976, 585 persons attending methadone maintenance clinics at East Coast veterans hospitals were enrolled in a survey of hepatitis antibody prevalence. Sera were tested for human immunodeficiency virus (HIV) and human T lymphotropic virus (HTLV) using both HTLV-I and HTLV-II immunoblots. Clinical and death records were also reviewed. None of the sera had HIV antibodies (upper 95% confidence limit, 0.5%); however, 103 (18%) had reactivity to HTLV. The profile of reactivity suggested that these subjects had been exposed to HTLV-II rather than to HTLV-I. Prevalence was as high in the early 1970s as today and correlated with duration of drug use rather than age. Neither cancers, specific neurologic diseases, nor excess deaths from any cause (overall 14%) could be ascribed to seropositivity. Therefore, HTLV (probably HTLV-II) has been a common infection of drug users for many years but adverse outcomes following infection were not demonstrated.