The influence of a non steroidal antiinflammatory drug (NSAID), ketoprofen, on the pharmacokinetics of two fluoroquinolone derivatives, pefloxacin (P) and ofloxacin (O), was studied in ten healthy adult male volunteers. The subjects were given orally for three days the quinolone alone (P: 400 mg q 12 h and O: 200 mg q 12 h), with at least a one week interval between the two quinolone studies. On day 4, the first kinetic study of pefloxacin and ofloxacin was performed. During the three following days, the quinolone was administered in association with ketoprofen (100 mg daily). Another pharmacokinetic study of P and O was performed on day 8 and the kinetic data obtained were compared to those found on day 4. During the two kinetic studies (D4 and D8), blood samples were taken at times 0, 1, 2, 3, 4, 6, 8, 10, 12 et 24 h and urine was collected during the time-periods 0-4 h, 4-8 h, 8-12 h and 12 24 h. Plasma and urine concentrations of the active P and O drug were measured by microbiological assay. Ketoprofen administered for three days with the fluoroquinolone derivative induced no statistical modification in the kinetic parameters of both P and O: peak plasma levels, time to peak level, areas under the curve, apparent volume of distribution, total and renal clearances.