The objective of this study was to compare the bioequivalence of 80 mg gliclazide in healthy Thai males. A single dose of each preparation was administered after an overnight fast in a 2-period crossover design with a 2-week washout period. Serial blood samples were collected over a period of 60 hours. Plasma gliclazide concentrations were determined using HPLC and the pharmacokinetic parameters were analyzed by noncompartmental analysis. Results: The median time to reach the maximal concentration (Tmax) for the test formulation was identical to that of the reference Diamicron (11.5 h). Similarly, the mean elimination half-lives (t1/2) for the test (20.4 ± 7.8 h) and Diamicron (21.5 ± 9.4 h) were comparable. Analysis of variance was carried out using logarithmic transformations of AUC0-∞ and Cmax as well as non-transformed Tmax. The mean (90% CI) of the difference in Tmax (h) was 0.08 ((-1.44) - 1.61). The mean (90% CI) of the AUC0-∞ and Cmax ratios for (test/reference) were 1.08 (0.98 - 1.18) and 1.09 (0.89 - 1.34), respectively. Since these values fall within the bioequivalence criteria, our study demonstrates bioequivalence of the 2 products.