Project MATCH (Matching Alcoholism Treatments to Client Heterogeneity) is a multisite collaborative project designed to evaluate patient-treatment interactions in alcoholism treatment. To evaluate whether major threats to the internal validity of the independent (treatment) variable in Project MATCH could be ruled out, we investigated several aspects of treatment integrity and discriminability. In this study, 1,726 alcohol-dependent participants at 10 sites were randomized to 3 treatments: cognitive-behavioral treatment (CBT), motivational enhancement therapy (MET), and 12-step facilitation (TSF). Participants received treatment either as outpatients or as aftercare following a more intensive inpatient or day hospital treatment. For both the outpatient and aftercare arms of the study, treatments were discriminable in that therapists implemented each of the treatments according to manual guidelines and rarely used techniques associated with comparison approaches. Participants received a high level of exposure to their study treatments, and the intended contrast in treatment dose between MET and the 2 more intensive treatments (CBT and TSF) was obtained. Alcoholics Anonymous involvement was significantly higher for participants assigned to TSF versus MET or CBT, whereas the treatments did not differ in utilization of other nonstudy treatments. Nonspecific aspects of treatment such as therapist skillfulness and level of the therapeutic alliance were comparable across treatment conditions.