We studied expressed prostatic secretions from 106 patients with prostatitis to determine the longitudinal course of prostatic fluid inflammation. Prostatic fluid specimens were collected from 14 patients with acute bacterial, 13 with chronic bacterial and 79 with abacterial prostatitis. White blood cells per high power microscopic field of the expressed prostatic secretion were counted under a cover slip. Inflammation in the expressed prostatic secretion was considered to be consistent with prostatitis if there were 10 or more white blood cells per high power field. The 14 patients with acute bacterial prostatitis had a mean of 10 visits with a mean followup of 59 months. Inflammation resolved within 1 month in 9 patients with acute bacterial prostatitis but it recurred in 5 other patients in association with urinary tract infection. The 13 patients with chronic bacterial prostatitis had a mean of 10 visits with a mean followup of 58 months. Episodic inflammation in the expressed prostatic secretion associated with urinary tract infection was seen in all patients during followup. The 79 patients with abacterial prostatitis had a mean of 7 visits with a mean followup of 40 months. Resolution of inflammation in the expressed prostatic secretion occurred in 9 patients (11%). Inflammation in the expressed prostatic secretion at followup was seen in 70 patients (89%), and 27 of the 79 patients (34%) had 10 or more white blood cells per high power field of expressed prostatic secretion in all subsequent specimens. In cases of abacterial prostatitis, neither the initial expressed prostatic secretion white blood count nor the presence of symptoms reliably predicted subsequent inflammation. The data suggest that prostatic inflammation resolves in most patients with acute bacterial prostatitis and is episodic in patients with chronic bacterial or abacterial prostatitis.