The effects of ibuprofen on bioavailability of ciprofloxacin were studied in rabbits. Animals were divided into three groups ; group A received 60 mg/kg of ciprofloxacin; group B and C received 60 mg/kg of ciprofloxacin with 60 and 240 mg/kg of ibuprofen, respectively. Ciprofloxacin and ibuprofen were given by single oral administration. Serum concentrations of ciprofloxacin were measured by high performance liquid chromatography with UV detector and pharmacokinetic parameters were calculated. Area under the serum concentrations versus time curve (${pm};S.E.$) of ciprofloxacin were decreased in group B and C compared with group A ($12.26;{pm};0.94$ and $12.57;{pm};0.94$ vs. $15.71;{pm};1.06;{mu}g{cdot}hr/ml$, p<0.05), whereas total clearances were increased ($1.81;{pm};0.13$ and $1.76;{pm};0.12$ vs. $1.40;{pm};0.09;l/hr/kg$, p<0.05). No significant differances in these parameters were observed between group B and C. Relative bio-availability of group B and C to group A were 78 and 80%, respectively. These results suggest that the coadministration of ibuprofen with ciprofloxacin may reduce the bioavailability of ciprofloxacin.