In the Beta-blocker Heart Attack Trial (BHAT) a number of strategies were implemented to increase the probability of informed voluntary consent among survivors of an acute myocardial infarction. To evaluate the subjects' comprehension of the study, a bioethicist conducted in-depth home interviews with a random sample of 64 participants from 11 geographic areas. The great majority of respondents proved to be well informed about the study design, its scientific logic, and possible risks of the experimental drug. However, five subjects (8% of the sample) appeared to believe they were involved in a therapeutic program rather than a research project. The analysis of predictor variables indicates that education, race, and age were associated with the degree of respondent awareness of fundamental aspects of the trial.