The influence of ketoprofen (K), a non steroidal antiinflammatory drug (NSAID) on the pharmacokinetics of two fluoroquinolone derivatives: ofloxacin (O) and pefloxacin (P) was studied in ten healthy adult male volunteers. All subjects orally received every 12 h the fluoroquinolone derivative (either O or P) for three days and the combination of the quinolone and ketoprofen (once a day) during the three following days. Two pharmacokinetic studies were performed for each quinolone, on days four and eight of the treatment. Blood samples were taken at times 0, 1, 2, 3, 4, 6, 8, 10, 12 and 24 h after dosing. Urine was collected during 4 time-periods: 0-4 h, 4-8 h, 8-12 h and 12-24 h. Plasma and urine concentrations of the active drug of O and P were measured by microbiological assay. Ketoprofen did not significantly modify the pharmacokinetic parameters of the two fluoroquinolones studied in terms of peak plasma levels, time to peak, area under the curve, elimination half-life, volume of distribution and total and renal clearances.