Many different interventions have been used to influence the prescribing behaviour of physicians, and qualitative evaluations (metaethnography) of such interventions have been reported. So far quantitative evaluations of such interventions have not been reported; this study is an attempt in that direction. Twenty-six published studies (January 1979-September 1991) on the interventions for influencing the prescribing behaviour of physicians were pooled and effect sizes were extracted. Mean effect size (Zr) was 0.559 and Cohen's d = 0.886. Estimated Fail-Safe N was 89. Success rates of interventions varied from 1% to 99%.