Information was gathered on 330 items, including demographic characteristics, life history, and lifetime and recent use of 14 substances. Results showed that those who abused only alcohol were older than those who had been multiple substance abusers. Alcohol and marijuana were the two drugs most commonly used to change the effects of other substances. Further research on individuals treated at the Eagleville Residential Combined Treatment Program in Eagleville, Pa. showed that outcomes in combined treatment of alcoholics and heroin users did not differ significantly from those resulting from separate treatment. In addition, heroin addicts who were also problem drinkers had significantly more social and psychological problems than those who were not problem drinkers. Finally, heavy drinking and problem drinking, both before and after admission to treatment for drug abuse, were associated with poorer treatment outcomes. Tables, figures, and 129 references.