A sample of 308 inmates admitted to KEEP at three Rikers houses between November 1988 and April 1990 who were not enrolled in methadone treatment at the time of their arrest were examined. 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 jail. Postrelease outcomes for methadone program participants were compared with outcomes for similar addicts who received 7-day heroin detoxification in jail. Multivariate analyses showed 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. Being in treatment at followup was associated with lower drug use and crime, but rates of retention in community treatment following release were modest. KEEP participants had more chronic and severe social and personal deficits than other addicts who applied for treatment. The in-jail program proved most effective in maintaining postrelease continuity of methadone treatment for inmates already enrolled in methadone at arrest. 3 footnotes, 9 tables, and 27 references