The main study examined inmates who were not enrolled in methadone at arrest. Eighty percent were drug injectors (usually both heroin and cocaine) who admitted committing an average of 117 property crimes and 19 violent crimes in the 6 months before being jailed. Methadone program participants' postrelease outcomes were compared with outcomes for similar addicts who received 7-day heroin detoxification in jail. Multivariate analyses indicated that program participants were more likely than controls to apply for methadone or other drug abuse treatment after release and to be in treatment at a 6.5-month followup. Moreover, being in treatment at follow-up was associated with lower drug use and crime, but rates of retention in community treatment after release were modest. KEEP participants have more chronic and severe social and personal deficits than other addicts applying for treatment. The in-jail program was most effective in maintaining postrelease continuity of methadone treatment for inmates already enrolled in methadone at arrest. The process evaluation yielded several recommendations to help overcome client-centered, administrative, and systemic obstacles to improved outcomes for this difficult-to-treat population of criminally involved addicts. 9 tables, 3 notes, and 26 references