We treated 15 men who had chronic bacterial prostatitis refractory to trimethoprim-sulfamethoxazole and/or carbenicillin with 400 mg. norfloxacin twice daily for 28 days. All pathogens were susceptible to norfloxacin and absent in prostatic fluid cultures obtained during therapy. One patient had negative post-therapy prostatic fluid cultures but was lost to followup at 1 month. Of the 14 patients followed for at least 6 months 9 (64%) were cured of the original infection, including 6 who have remained uninfected and have had negative prostatic secretion and urine cultures for at least 2 years (1), 1 year (2) or 6 months (3). In 3 patients urinary tract infections recurred with new pathogens at 6, 560 and 820 days after post-therapy negative prostatic fluid cultures. Bacterial prostatitis with the original pathogen recurred in 5 patients within 2 months of completing therapy. The bacteria remained susceptible to norfloxacin but could not be eradicated with 30 to 90 days of additional norfloxacin therapy. Cures were achieved in 9 of 12 patients with Escherichia coli, none of 2 with Pseudomonas prostatitis and 3 of 5 with prostatic calculi. No patient experienced significant adverse effects. The data suggest that norfloxacin is effective and safe for the treatment of refractory chronic bacterial prostatitis.