A meta-analysis of 16 educational interventions and 10 needle exchange programs was performed to estimate the effectiveness of reducing HIV risk behaviors in the injecting drug user population. Information on intervention, outcome, design and demographics was coded and analyzed for all educational and needle exchange program evaluation studies published between January 1984 and May 1995. The weighted mean effect size for the 6,251 study subjects of the 16 educational interventions was 0.749 (95% CI, 0.708 to 0.790), and the weighted mean effect size for the 1,675 study subjects of the 10 needle exchange programs was 0.279 (95% CI, 0.207 to 0.352), suggesting that both interventions had a positive impact on reducing HIV risk behaviors associated with injecting drug use. However, these results were dependent upon research design, outcome type and follow-up time.