Aims. To test the hypothesis that drug law enforcement encourages entry into methadone maintenance treatment. Design. Survey conducted as face-to-face interviews in methadone clinics, at needle exchange centres and on the street, in areas of widespread heroin dealing and use. Setting. Sydney, Australia. Participants. Heroin users. Measurements. Self-reported data on personal characteristics, and experience of drug law enforcement and methadone maintenance treatment. Findings. Although keeping their relationship/family together emerged as the most important reason given by respondents for entering treatment, avoiding more trouble with police/courts was also rated by the majority of respondents as an important or very important reason for entering treatment. The results of logistic regression analysis show that, after controlling for other factors, heroin users who have had a friend or family member imprisoned are more likely to have tried methadone maintenance treatment. A heroin user's own experience of arrest and imprisonment was also found to increase the likelihood of having tried treatment but only when age and length of time as a regular user (which were related to the user's experience of arrest and imprisonment) were excluded from the set of control variables. Despite having extensive histories of contact with the police and criminal justice system, however, Asian, Middle Eastern and Aboriginal respondents showed less proclivity to enter treatment than Caucasian respondents. Conclusion. Drug law enforcement may have a role to play in heroin demand reduction but its effects are not evident for all ethnic groups and the separate effects of contact with police, age and time spent in the heroin market remain unclear.