Serum and prostatic tissue concentrations of lomefloxacin were measured in 12 elderly patients who underwent transurethral resection of the prostate after receiving a single oral dose of 400 mg. The peak serum concentration of lomefloxacin was 2.5-10.0 micrograms/mL (mean, 5.2 +/- 1.9 micrograms/mL). During surgery, serum and tissue concentrations averaged 4.6 +/- 2.2 micrograms/mL and 6.5 +/- 2.7 micrograms/g, respectively. The ratio of tissue to serum concentrations was 1.53 +/- 0.54. The levels of lomefloxacin in serum and prostatic tissue were found to be higher than the minimum inhibitory concentration (MIC) values for most urinary tract pathogens.