Serial biannual cross-sectional assessments of HIV sexual risk indicated a consistent increase in safer sexual practices among homosexual men participating in the Chicago-Multicenter AIDS Cohort Study (MACS)/Coping and Change Study (CCS) in 1986-1988. Safer sexual practices were achieved by avoidance of anal sex and less often by consistent use of condoms. Longitudinal patterns of variability in individual behavior were also assessed. After 1 year of follow-up, 53% of the participants maintained safer practices in receptive anal sex, 6% maintained unsafe practices, while 31% relapsed at least once. After 2 years, 45% maintained safer practices, 3% maintained unsafe practices and 47% relapsed at least once. Similar trends were observed in insertive anal sex.