Concentrations of cefotaxime (CTX) in serum and prostatic tissue were studied in human and rat. CTX kept high level of 40 to 100 micrograms/g in prostatic tissue at least as long as 2 hours following intraperitoneal injection in a dosis of 100 mg/kg of body weight in rat. Patients intravenously injected of 1 g of CTX showed the activity of 6.8 +/- 4.1 micrograms/g in prostatic tissue.