We have conducted a study on the antibacterial activity and penetration into prostatic and renal tissue of cefpirome (CPO), a new injectable cephalosporin drug, and have obtained the following results. In the target bacterium Neisseria gonorrhoeae stored in this Department (34 non-PPNG isolates, 20 PPNG isolates), the minimum inhibitory concentration (MIC) distribution of CPO was < or = 0.003-0.1 micrograms/ml for the non-PPNG isolates and 0.006-0.1 micrograms/ml for the PPNG (penicillinase-producing Neisseria gonorrhoeae) strains, with MIC90 values of 0.1 microgram/ml and 0.05 microgram/ml respectively. Concentrations in blood and in prostatic tissue were measured in 30 prostatectomy patients after intravenous injections of 1 g of CPO. The concentration in prostatic tissue reached a maximum of 52.9 micrograms/g 15 min after administration, and gradually decreased thereafter, with average values of 17.9 micrograms/g at 60 min, 10.3 micrograms/g at 180 min, 7.22 micrograms/g at 320 min (one patient) and 2.70 micrograms/g at 360 min (one patient). There was a positive correlation between prostatic tissue concentration and blood concentration at the time of tissue collection, and it is considered that CPO penetrated into the prostatic tissue to an extent dependent on its concentration in the blood. In renal tissue, measured in 4 nephrectomy patients, the CPO concentrations found were 107-148 micrograms/g in the cortex and 80.6-88.6 micrograms/g in the medulla, which were higher than the blood concentration levels in all of the subjects. These findings indicate that CPO showed sufficient concentrations in the blood and tissues for it to be considered highly useful in the treatment of urological infections.