It has been estimated that as many as 75% of individuals treated for substance abuse relapse within 90 days after completion of treatment. Studies of relapse have typically defined the problem as a return to the specific substance for which the individual was originally treated. Because multiple substance appears to be common, this study examined relapse using a broader definition of relapse--the abuse of any substances after previous treatment. It investigated determinants of relapse and antecedents of recent use for 30 substance abusers re-entering in-patient treatment. A structured interview assessment revealed that the patients relapsed within 2 months following previous treatment, yet waited 2.7 years before re-entering treatment. Alcohol was often the initial substance used after previous treatment. More than one-half of the subjects indicated that intrapersonal negative emotional states, such as loneliness or depression, led to the relapse. An even greater percentage of respondents indicated that such determinants were antecedents to recent use. Implications for treatment are presented. (Author/NB)