Acute bacterial prostatitis caused by common urinary tract pathogens is an infrequent disease, and diagnostic difficulties are rarely encountered. On the other hand, chronic prostatitis is a common disease requiring rather elaborate diagnostic procedures. We applied the localization protocol of the four-specimen technique and combined quantitative determinations of microorganisms and quantitative cytologic analysis plus, in chlamydial infections, serologic investigations. Our studies provide good evidence that Ureaplasma urealyticum and Chlamydia trachomatis must be considered etiologic agents in many cases of chronic bacterial prostatitis. These unconventional microorganisms are assumed to infect the prostate by way of intracanalicular ascension from the urethra.