The aim of this project is to conduct a multi-site effectiveness study to determine whether the addition of a monthly injection of depot naltrexone to treatment as usual (TAU) will significantly improve outcome in parolees and probationers with a history of opioid addiction compared to TAU alone. Participants will be randomized to either treatment as usual in community programs or monthly injections of depot naltrexone for six months with treatment as usual in community programs. The effectiveness of depot naltrexone has never been studied in opioid dependent parolees. all parolee subjects will be evaluated at baseline, while in treatment, and at 6, 12 and 18 month post entry time points. The primary study outcomes are retention in treatment, drug use, re-arrests, psychosocial and medical/psychiatric functioning, and economic costs and benefit costs of naltrexone.