The concentration of Lomefloxacin (NY-198), a new quinolone, in human prostatic tissue and fluid was examined. Lomefloxacin was concentrated in prostatic gland and the mean ratios of prostatic tissue levels to serum levels (P/S) were 1.39-1.83 during 2 to 6 hrs after administration. Concerning prostatic fluid concentrations, there were no significant differences between healthy volunteers and patients with chronic prostatitis. The mean ratios of prostatic fluid levels to serum levels (Pf/S) were 0.36-0.77 during 1 to 4 hrs after administration. The concentration of Lomefloxacin in the prostatic tissue and fluid is high enough to eradicate the majority of pathogens causing bacterial prostatitis.