The concentration of Cefbuperazone (CBPZ) were determined by bioassay in the serum and prostatic tissue of 36 patients with benign prostatic hypertrophy, who underwent transurethral resection. One gram of CBPZ was injected intravenously prior to surgery. Pharmacokinetic analysis was performed using the two or three compartment model theory. The maximum serum level of CBPZ was 82.2 micrograms/ml at 30 min after the start of CBPZ administration and biological half-life was 97.3 min. CBPZ concentration in prostatic tissue reached a maximum level of 26.3 micrograms/g at 50 min following CBPZ administration. The prostatic tissue level was 28-40% of the serum level. These results suggested that intravenous administration of CBPZ would be extremely effective against pathogenic bacteria, particularly Enterobacter, E. coli, Klebsiella, Serratia, Proteus and Bacteroides, judging from its prostatic concentration.