Abstract: Ninety serum samples of gentamicin were determined by fluorescence polarization immunoassay (FPIA) and microbiological assay (MA) and the results were compared. Liner regression analysis showed that the two methods were highly correlated with a correlation coefficient of 0.98. The mean concentration of gentamicin as determined by MA method was significantly higher than that by FPIA method. Serum concentration-time data derived from 5 patients were fitted to a one-compartment model. No significant differences in the pharniacokinetic parameters and estimated dosages were observed. The FPIA method was shoran to be as correct and reliable as the MA method in estimating gentamicin pharmacokinetic parameters.