The effects of commitment to abstinence and acute stress on return to drug use were examined in a study of treated alcoholics, opiate users, and cigarette smokers (N = 221). Subjects were followed for 12 weeks or until they used their problem drug for 7 consecutive days. Commitment to absolute abstinence at end of treatment was related to a lower risk of returning to use and longer time between the first use and relapse. Withdrawal symptoms and negative and positive moods predicted first drug use, but only when assessed retrospectively. Prospective analyses failed to reveal a link between these variables and return to use. These findings suggest a reevaluation of current models of relapse. Acute stress may be less important in precipitating return to drug use than previously believed.