Despite the harm that cocaine can cause to the body, its abuse is widespread. It is the cause of more visits to hospital emergency rooms nationwide than any other illegal drug. Effective treatments for cocaine and opiate addictions are essential to the decline of cocaine- and opiate-related disorders. Unfortunately, cocaine use remains prevalent among participants in many opioid maintenance programs. The addition of other medications to methadone maintenance may prove helpful in reducing cocaine use. Disulfiram, a drug used to treat chronic alcoholism, causes unpleasant effects when even small amounts of alcohol are consumed. This study will evaluate the effectiveness of three different doses of disulfiram in treating cocaine dependence in opioid- and cocaine-dependent individuals maintained on methadone.