This paper examines a unique finding from a larger research study of methadone maintenance treatment at four treatment programs in three Northeastern states. In looking at methods used by narcotics addicts to withdraw or detoxify from heroin, we found a small group of persons who had successfully detoxified from heroin addiction using a structured injection regimen of gradually decreasing amounts of heroin and gradually increasing amounts of cocaine. While this paper represents the case study of ten cases, the regimen was reported by others as part of 'street pharmacology.' It is a relatively uncommon regimen, reportedly due to the expense of the procedure and the problems associated with cocaine abuse. It is the pharmacological aspects of the procedure which warrant attention. All ten cases reported little or no withdrawal symptoms after the last injection containing small amounts of heroin. It was widely believed that cocaine interacts with heroin in a way which masks withdrawal during the detoxification process, providing a measure of physiological relief. Information from the addict world on that interaction provides clues as to the biochemical properties of drug interactions and may suggest areas for further clinical and pharmacological research.