The cefoperazone and sulbactam concentrations in human prostatic fluid were measured following intravenous administration of sulbactam/cefoperazone (SBT/CPZ) and its clinical efficacy and safety in the treatment of 11 patients with acute or chronic bacterial prostatitis were evaluated. Cefoperazone concentrations in prostatic fluid (PF) one hour after an intravenous infusion of SBT/CPZ at a dose of 1 g and 2 g were 0.57 +/- 0.26 micrograms/ml and 1.37 +/- 0.86 micrograms/ml, respectively, both exceeding the MIC against most of the isolated strains from expressed prostatic secretion (EPS). The sulbactam levels in PF at doses of 1 g and 2 g of SBT/CPZ were 0.30 +/- 0.18 micrograms/ml and 0.38 +/- 0.13 micrograms/ml, respectively, both of which were high enough to potentiate antimicrobial activity of cefoperazone. The peak of MIC distribution of sulbactam/cefoperazone against E. coli (14 strains) and S. epidermidis (21 strains) isolated from EPS of patients with bacterial prostatitis was in a range of 0.1-0.2 micrograms/ml and 0.2-0.78 micrograms/ml as described for the cefoperazone concentration, respectively, which were superior to those of cefoperazone, ceftazidime and piperacillin, all compared as control, SBT/CPZ exhibited 8 fold or more potent antimicrobial activity than cefoperazone against beta-lactamase producing E. coli and CNS. Clinically, SBT/CPZ was given to 11 patients diagnosed as having bacterial prostatitis in a daily dose of 2-4 g for 5 to 8 days. The drug was found to be effective in all (100%) of 5 patients with acute prostatitis and in 3 (75.0%) of 4 patients who were judged to be assessable among 6 chronic patients. No side effects of any kind were observed in any of the patients treated. In laboratory tests, a transient thrombocytopenia was reported for one patient. SBT/CPZ is particularly useful in the treatment of acute bacterial prostatitis caused by GNR. This drug is useful for chronic prostatitis those, caused primarily by CNS which is susceptible to this agent. This drug is available as an injectable form, subjects for its appropriate usage will be those who show acute exacerbation of infection or who do not respond to oral therapy.