Bioequivalence focus on the release of a drug substance from its dosage form and subsequent absorption into the systemic circulation. Atenolol is a beta1-selective (cardioselective) beta-adrenergic receptor blocking agent without membrane stabilizing or intrinsic sympathomimetic activities. Objective was to assess the bioequivalence of test and reference formulations of atenolol 100 mg tablets. This open label, single-dose, randomized, 2-period, crossover oral bioequivalence study was conducted in 26 healthy human adult subjects under fasting condition. Subjects received atenolol 100 mg of either test or reference formulation with a washout period of 7 days. After study drug administration, serial blood samples were collected over a period of 24 h. The plasma levels of atenolol were determined by a validated method using LC/MS/MS. Pharmacokinetic (PK) parameters Cmax, Tmax, t1/2, AUC0-t, AUC0-infinity and kel, were determined for test and reference formulations. The formulations were to be considered bioequivalent if the log-transformed ratios of Cmax, AUC0-t and AUC0-infinity were within the predetermined bioequivalence range of 80% to 125%. A total of 26 subjects were enrolled. No significant differences were found based on anal. of variance, with mean values and 90% confidence intervals of test/reference ratios for these parameters as follows: Cmax, 833.78 vs. 785.36 ng/mL (96.21-120.65); AUC0-t, 6608.29 vs. 6250.15 ng·hr/mL (98.77-117.80); and AUC0-infinity, 7061.50 vs. 6651.60 ng·hr/mL (99.41-117.99). In these healthy subjects, results from the pharmacokinetic anal. suggested that the test and reference formulations of atenolol 100 mg tablet are bioequivalent.