Typically, drug addicts show high incidence rates of offending and are responsible for a substantial proportion of muggings and other offenses committed in cities like Zurich. Although delinquency often precedes drug addiction, drug addiction increases the incidence and seriousness of offending. The medical prescription of heroin to drug addicts may reduce the number of offenses and thereby contribute to general crime reduction. To evaluate whether heroin prescription produced any reduction in individual offending rates, several measures were used to compare offending rates before and during the prescription period: conviction records, police records, and extensive interviews conducted every 6 months using instruments measuring self-reported offending and victimization. Preliminary findings did not clearly demonstrate the effectiveness of heroin prescription programs in relation to different drug addict careers. Methods used to assess the effect of heroin prescription programs on individual offending rates are detailed. Additional research is recommended to explore the stability of social adjustment and the reduction of offending with heroin prescription programs. 29 references and 3 figures