A series of 60 patients with a diagnosis of chronic abacterial prostatitis, as defined by the Stamey procedure, was studied by transrectal prostatic ultrasound and subsequent transperineal biopsy of the abnormal areas of the prostate in order to ascertain the role of micro-organisms in this condition. Histological assessment revealed a chronic inflammatory infiltrate, generally of low grade, in 53 patients (88%). Organisms were isolated from the prostatic tissue of only 9 patients (15%) and were considered to be contaminants from the perineal skin, since treatment with an appropriate antimicrobial agent failed to alter symptoms or affect the leucocyte count in the urine or prostatic fluid. Chronic abacterial prostatitis may be a non-organismal inflammatory process.