We surveyed the 270 survivors of acute myocardial infarction who refused to participate in the Warfarin Re-Infarction Study (WARIS). Information on medical variables were derived from registration forms completed by hospital staff upon discharge, whereas data on a variety of health conditions and reasons for refusal were gathered by mailed questionnaires, 178 (66%) of which were returned. Some disparities were found when comparing non-respondents and participants, the former showing more potential bad risk factors. The diversities between participants and non-respondents are of yet unknown prognostic importance. However, the presence of such differences imply that information on characteristics of non-respondents in clinical trials is desirable in terms of generalizability of the trial results. Reasons stated for non-participation reflect poor motivation, low mobility and saturation with focusing on disease. A slight co-variation between social status and reasons for refusal was noted.