The objective of this study was to assess the bioequivalence between the omeprazole laboratory based formulation and the commercial formulation, Zimor Rubio, Spain, considered as reference formulation. The experiment was carried out according to a 2-period, 2-sequence crossover design with a two week washout period. A validated high performance liquid chromatographic method was applied for in vivo experiments. It was observed that omeprazole contents were comparable in all formulations. To establish bioequivalence, 90% confidence intervals (CI) for the differences of total AUCs of the test and reference formulations were calculated. The 95% CI ratio of the AUC within 0.80 to 1.25 was considered as bioequivalent. The carryout effect was investigated prior to assessing the bioequivalence of the two formulations. The test formulation of omeprazole was found to be comparable with the reference formulation (Zimor) with regard to bioavailability.