The relative bioavailability of a new 750 mg tablet formulation of ciprofloxacin (test formulation supplied by Dr. August Wolff GmbH and Co., Germany) was compared with that of Ciprobay tablets 750 mg (reference formulation from Bayer Vital GmbH and Co., Germany). Twenty-four healthy volunteers (12 male and 12 female) were included in this single-dose, 2-sequence, crossover randomized study. Blood samples were obtained prior to dosing and at 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 18, 24 and 30 hours after drug administration. Plasma concentrations of ciprofloxacin were determined by HPLC. No differences were found when the in vitro dissolution profiles of both formulations were compared. The pharmacokinetic parameters AUC(0-t), AUC(0-infinity), Cmax and Cmax/AUC(0-infinity) were tested for bioequivalence after log-transformation of data, and ratios of tmax were evaluated nonparametrically. The parametric analysis revealed the following mean values for the test/reference ratios (90% standard confidence intervals in parenthesis (ln-transformed data): 1.01 (0.95-1.07) for AUC(0-t), 0.99 (0.93-1.05) for AUC(0-infinity), 1.05 (0.97-1.14) for Cmax and 1.06 (0.97-1.15) for Cmax/AUC(0-infinity). The nonparametric confidence interval for tmax was 0.77-1.15. All parameters showed bioequivalence between both formulations as their confidence intervals were within the bioequivalence acceptable range of 0.80-1.25 limits; the 90% confidence interval for tmax slightly exceeded limits of bioequivalence. We conclude that both formulations show bioequivalence for both the rate and the extent of absorption.