The bioavailability of two formulations of atenolol was compared in an open, randomized crossover study. Each film-coated tablet contained 100 mg of active drug. The plasma concentrations of atenolol were determined using a newly developed and specific high-performance liquid chromatography procedure. The areas under the concentration-time curves (AUC) were calculated, as were pair differences and ratios for individual AUC values and for maximum plasma levels. The latter were determined (Cmax.(m] and calculated (Cmax.(c] at the corresponding time values (tmax.) for test and reference formulations, and were then tested for statistical significance. The 95% confidence limits for both test and reference preparations, taken according to Westlake or Wilcoxon, were found to be 80.0-114.7% for AUC, 80.2-119.9% for Cmax. and 74.5-132.8% for tmax. In terms of pharmacokinetic target criteria, therefore, it can be seen that there were no substantial differences between the two film-coated tablets. The two atenolol preparations, therefore, may be classified as bioequivalent.