 Scientific goals. The primary goal is to determine if simultaneous abstinence from heroin and cocaine can be elicited by combining two approaches: flexible methadone dosing and voucher-based CM. Secondary goals include: 1 comparing saliva and plasma levels of methadone, cortisol, and prolactin as predictors of treatment outcome; and 2 evaluating the impact of methadone maintenance on renal function, lipid profile, and cardiac function. 