The abuse of drugs by alcoholics, the abuse of alcohol by drug abusers, the prevalence of alcohol abuse in polydrug clients, and the role of alcohol as a steppingstone are examined quantitatively over the past decade. The increase of drug abuse by alcoholics and the increase of alcohol abuse and alcoholism by polydrug abusers is documented. This is accounted for mainly by an increase of drug abuse in younger and/or female alcoholics. The abuse of alcohol by heroin addicts has also increased, particularly when heroin purity diminishes and when these clients cycle through methadone maintenance. However, much of the alcoholism in these patients began prior to the onset of heroin use and dependence. Methods of treatment modifications necessary to deal with problems presented by these combinations are discussed.