The bioavailability of two suspension formulations of potassium diclofenac (Flogan, Merck and Cataflam, Ciba-Geigy) were compared in eighteen healthy male volunteers who received a single dose of 7 ml of each suspension (equivalent to 105 mg of potassium diclofenac) in an open randomized two period crossover design, with a fourteen-day washout period between doses. Serum samples were obtained over a 24 hour interval and diclofenac concentrations were determined by HPLC with ultraviolet detection. From the serum diclofenac concentration vs time curves, AUC[0-24] (area under the concentration vs time curves from 0-24 h), Cmax (maximum achieved concentration), Tmax (time to achieve Cmax) and Ke (terminal first order elimination constant) were obtained. Overlapping of Tmax intervals for both formulations was observed, but the important inter-subject variation observed in Cmax ratios did not allow equivalence conclusion for the rate of absorption. Equivalence in the extent of bioavailability between both potassium diclofenac suspension brands was concluded from the analysis of AUC[0-24] ratios.