The bioavailability of a chlorpropamide tablet formulation chlorpropamide tablet formulation was assessed by comparing it to a reference suspension of chlorpropamide. Eighteen healthy adult men received chlorpropamide 250 mg as a tablet (Diabinese, Pfizer) and suspension in an open two-way crossover study of Latin-square design with a 14-day washout period between treatments. Serial blood samples were obtained by venipuncture for 96 hours for chlorpropamide serum concentration determinations. Serum glucose concentrations were determined at 0, 0.5, 1, 2, and 4 hours. The area under the serum chlorpropamide concentration-time curve (AUC), peak serum chlorpropamide concentration (Cmax), time to Cmax, and mean glucose concentration at each time point for each treatment were compared using a two-tailed Student's t test for paired data (p less than 0.05). Microrate constants for a two-compartment model for oral absorption computed using nonlinear regression were also compared. There were no significant differences between the two formulations regarding AUC, Cmax, time to Cmax, and hypoglycemic response. The absorption rate for the tablet was significantly greater than for the suspension. The results suggest that the oral chlorpropamide tablet and reference suspension are bioequivalent. Although the tablet had a faster absorption rate than the suspension, this probably is not clinically important since both formulations similarly decreased serum glucose concentration.