Project MATCH is a national, randomized clinical trial of alcoholism treatment matching. The generalizability of Project MATCH has been questioned, as well as efficacy trials in general. This study investigates at one site whether there were differences between clients who participated in MATCH and others not entered into the study. Significant differences were found on three inclusion/exclusion related variables: plans to move, available transportation, and locator provision. Significant but rather small differences were also found on age and education. There were no significant differences on a large number of demographic and problem severity measures. In addition, the Alcohol Use Disorders Identification Test scores suggest that those included in the MATCH sample actually had more serious alcohol involvement than those who were ineligible or declined participation. Overall, the differences found do not appear to threaten the generalizability of the study.