The spectrum of chronic bacterial prostatitis (CBP) comprises Gram-negative, Gram-positive and atypical pathogens. Because of its broad spectrum of activity, moxifloxacin might be a suitable antibiotic for the treatment of CBP. In this pharmacokinetic study, plasma concentrations and the penetration of moxifloxacin into prostatic fluid and ejaculate were investigated. Twelve healthy male volunteers received a single oral dose of 400mg moxifloxacin and at the same time received 3.24 g of iohexol intravenously to assess urinary contamination of prostatic fluid and ejaculate. Plasma concentrations were determined at 0, 0.5, 1, 2, 3 and 4h and prostatic fluid and ejaculate (mean+/-standard deviation (S.D.)) were determined at 3.5+/-0.4h and 3.6+/-0.4h, respectively, following administration of drugs. Urinary concentrations were determined in the urine collected from 0-4.5h. Concentrations of moxifloxacin and iohexol in plasma, secretions and urine were determined by high-performance liquid chromatography. The mean+/-S.D. peak plasma concentration of moxifloxacin was 2.8+/-0.5 mg/L observed after 1.6+/-0.9h. In prostatic fluid, the concentration of moxifloxacin was 3.8+/-1.2 mg/L and the prostatic fluid/plasma ratio was 1.6+/-0.5. In ejaculate, the concentration was 2.5+/-0.7 mg/L and the ejaculate/plasma ratio was 1.0+/-0.2. Moxifloxacin concentrations in prostatic fluid were ca. 60% (P<0.05) higher than in plasma and concentrations in ejaculate were approximately the same as in plasma. Therefore, moxifloxacin might be a good alternative for the treatment of CBP, but further studies are warranted to establish this indication.