Summary—In patients with chronic abacterial prostatitis, a double‐blind trial of 3 months of treatment with minocycline 100 mg twice daily compared with diazepam 5 mg twice daily was undertaken.The percentage fall in polymorphonuclear leucocyte counts in the expressed prostatic secretions was much more marked after treatment with minocycline than with diazepam. Over a follow‐up period of at least 12 months, further treatment was necessary in more patients originally treated with diazepam than with minocy