To examine the effect of reinforcer density in prize-based abstinence reinforcement, heroin/cocaine users (N = 116) in methadone maintenance (100 mg/day) were randomly assigned to a noncontingent control group (NonC) or to 1 of 3 groups that earned prize draws for abstinence: manual drawing with standard prize density (MS) or computerized drawing with standard (CS) or high (CH) density. Probabilities (prizes/draw) were standard (50%) and high (78%); prize density was double blind. Mean prize values were CH, $286; CS, $167; MS, $139; and NonC, $171. Outcomes were % opioid/cocaine-negative urines during the 12-week intervention and then 8 weeks postintervention as well as diagnosis of dependence up to 6 months poststudy. CH had significantly more negative specimens than did NonC during intervention and had more than all groups during postintervention treatment: Mean % negative (95% confidence interval) during postintervention treatment adjusted for baseline drug use and dropout were CH, 55% (14%-90%); CS, 7% (1%-27%); MS, 4% (1%-12%); and NonC, 3% (1%-10%). Current cocaine dependence diagnoses after treatment were significantly lower in contingent compared with noncontingent groups. Computerized drawing with higher-density prizes enhanced reduction of cocaine use; abstinence reinforcement had long-term therapeutic benefits.