 Benefits. Participants will receive methadone, counseling, and some medical care at no charge. The methadone and voucher interventions are likely to reduce participants use of heroin and cocaine. Counseling will include management of HIV risk behaviors. The study incorporates participant safety monitoring and will provide information relevant to improving the health and safety of community methadone-maintenance patients. The pharmacokinetic-pharmacodynamic part of the study does not benefit participants directly, but may lead to the development of more useful and less invasive drug-monitoring methods. 