Gatifloxacin (GTX), a new fluoroquinolone with extended antibacterial activity, is an interesting candidate for the treatment of chronic bacterial prostatitis (CBP). Besides the antibacterial spectrum, the concentrations in the target tissues and fluids are crucial for the treatment of CBP. Thus, it was of interest to investigate its penetration into prostatic and seminal fluid. GTX concentrations in plasma, urine, ejaculate, prostatic and seminal fluid, and sperm cells were determined by a high-performance liquid chromatography method after oral intake of a single 400-mg dose in 10 male Caucasian volunteers in the fasting state. Simultaneous application of the renal contrast agent iohexol was used to estimate the maximal possible contamination of ejaculate and prostatic and seminal fluid by urine. GTX was well tolerated. The means (standard deviations) for the following parameters were as indicated: time to maximum concentration of drug in serum, 1.66 (0.91) h; maximum concentration of drug in serum, 2.90 (0.39) g/ml; area under the concentration-time curve from 0 to 24 h, 25.65 g ⅐ h/ml; and half life, 7.2 (0.90) h. Within 12 h about 50% of the drug was excreted unchanged into the urine. The mean renal clearance was 169 ml/min. The gatifloxacin concentrations in ejaculate, seminal fluid, and prostatic fluid were in the range of the corresponding plasma concentrations which were 1.92 (0.27) g/ml at approximately the same time point (4 h after drug intake). The concentrations in sperm cells (0.195, 0.076, and 0.011 g/ml) could be determined in three subjects. The good penetration into prostatic and seminal fluid, the good tolerance, and the previously reported broad antibacterial spectrum suggest that GTX may be a good alternative for the treatment of chronic bacterial prostatitis. Clinical studies should be performed to confirm this assumption.Fluoroquinolones have already been used successfully in the treatment of chronic bacterial prostatitis (CBP) and are recommended as first-line treatment for this indication (1, 6). This recommendation is based on their antibacterial activity; on their ability to penetrate into prostatic tissue, prostatic fluid, seminal fluid, and ejaculate; and on clinical studies (6). Although in about 60% of patients with symptoms of chronic prostatitis significant prostatic inflammation can be demonstrated (4), an etiologically recognized pathogen, such as Escherichia coli, Klebsiella spp., Proteus spp., Enterococcus faecalis, or Pseudomonas aeruginosa, is only isolated in up to 10% of these patients (14). In the vast majority of patients, bacterial evaluation either fails to identify a pathogen (nonbacterial prostatitis), or identifies so-called atypical bacteria, like Mycoplasma spp., Ureaplasma spp., and Chlamydia spp. These atypical pathogens are, however, not well covered by the antibacterial activity of the classical fluoroquinolones, e.g., ciprofloxacin or ofloxacin. Thus, the treatment of CBP remains a challenging issue, and new fluoroquinolones with improved antibacterial acti...