<qa>  What is the main outcome measure of the drug-abusing opioid-dependent outpatientsMethods. During an initial 6-week baseline phase, cocaine-abusing opioid-dependent outpatient participants 300 enrolled; 180 evaluable will be stabilized on methadone 70 mgday. At the end of baseline, participants who continue to use heroin and cocaine will be randomized to one of two dosing regimens and one of two CM conditions. In the flexible-dose regimen, participants will receive individualized dose increases 15 mgday to a maximum of 190 mg day, based on heroin use and withdrawal. In the fixed-dose regimen, participants methadone dose will be increased to 100 mgday and remain fixed there. Dose-group assignment will be double-blind: investigators will determine participants individualized dose increases, but only the pharmacists will know which participants actually receive them. The two CM conditions will be: vouchers contingent on cocaine-negative urine specimens, or noncontingent vouchers i.e., vouchers independent of urine cocaine screen results. The main outcome measure will be the percentage of urines simultaneously negative for both cocaine and illicit opiates during treatment. For the concurrently run pharmacokinetic-pharmacodynamic portion, saliva and blood samples will be taken at regular intervals to determine levels of methadone, cortisol, and prolactin as predictors of treatment outcome. For the concurrently run medical-outcomes portion, urine renal function, blood lipid profile, and ECGs cardiac function,will be obtained at set intervals. 