Twelve male patients with impaired renal function and six healthy male volunteers were given a single i.v. dose of cefotaxime (1000 mg). Serum concentrations of cefotaxime were determined by a microbiological assay. The pharmacokinetic parameters were obtained using an open two-compartment model. Results showed that the median elimination t1/2 of cefotaxime was prolonged in patients (3.25 h) compared to volunteers (1.4 h) (P less than 0.001). The median AUC0----infinity was increased in patients (211.99 micrograms/ml X h) compared with volunteers (78.21 micrograms/ml X h) (P less than 0.001). Also, the median clearance was decreased in patients (4.73 l/h) compared with volunteers (12.82 l/h) (P less than 0.001). This study shows prolonged half-life and decreased elimination of cefotaxime in patients with impaired renal function.