Traditionally, researchers and clinicians have viewed street heroin users as representing an end point in a drug-using career. It is toward this population that major national treatment efforts have been directed. Concomitant with the historical national concern about heroin use has been concern about the increase in crack cocaine use. There has been speculation that crack use may have become a substitute for the higher risk of heroin injection. This article examines the impact of crack use in a national population of heroin users. It was consistently found that there was a correlation between the frequency of crack use and the frequency of speedballing as well as the use of other forms of cocaine, amphetamines, and marijuana. There was als...