A bioequivalence study of 2 oral formulations of 500 mg tablets of ciprofloxacin was carried out in 24 healthy volunteers according to a single dose, two-sequence, crossover randomized design. Blood samples were taken prior to each administration and at 13 points within 32 hours after the dose, and plasma concentrations of ciprofloxacin were determined by HPLC. The pharmacokinetic parameters Cmax and tmax were obtained directly from plasma data, ke was estimated by log-linear regression, and AUC was calculated by the trapezoidal rule. The pharmacokinetic parameters AUC and Cmax were tested for bioequivalence after log-transformation of data, differences of tmax were evaluated nonparametrically. The 90% standard confidence intervals of the mean values for the test/reference ratios were 0.87-0.97 for AUC and 0.91-1.05 for Cmax, within the bioequivalence acceptable range of 0.80-1.25 limits. So, we conclude that both formulations were found bioequivalent and, therefore, interchangeable.