The study sample was recruited from six methadone maintenance outposts and at a weekly sexually transmitted diseases clinic for drug-using prostitutes. Both IV and non-IV drug users were invited to participate in the study. A blood sample for HIV serology was taken, and participants were interviewed with a standard questionnaire. Participants returned for followup examinations and interviews every 4 months. A total of 622 subjects who had ever used drugs intravenously participated in the study between January 1986 and December 1989. HIV-antibody seroprevalence in annual samples of injectors was constant over the years 1986-89; HIV-antibody incidence in a cohort of injectors apparently decreased from 1986 to 1987 and stabilized after that until 1989. Acute hepatitis B incidence in all drug users in Amsterdam declined rapidly between 1985-89. Changes in drug-use behavior so far apparently have resulted in a stabilization of the epidemic among injectors at a level that is still a high incidence rate of 5-6 per 100 person-years. 1 table, 2 figures, and 17 references