The role of comparative bioavailability trials in testing for the bioequivalence of different formulations of a drug was discussed and the statistical aspects of the design and analysis of such trials were reviewed. The design of such trials presented no special problem, but the customary method of analysis, which tests the null hypothesis of no difference between formulations, was irrelevant to the central purpose of such trials, which was to determine whether the formulations have essentially equivalent therapeutic effects. Only those characteristics of the data that possess a meaningful relation to the therapeutic use of the drug should be analyzed and estimation procedures rather than hypothesis testing techniques should be employed. Several aspects of the statistics of bioavailability trials which require further investigation were listed.