A total of 388 patients with symptoms of chronic prostatitis and inflammatory findings in expressed prostatic secretion (EPS) or in a urine sample collected immediately after prostate massage, were examined over a 2 year period at the Outpatient Department for Urogenital Infections, University Hospital for Infectious Diseases 'Dr Fran Mihaljević', Zagreb, Croatia. The infective aetiology was determined in 276 (71.13%) patients. Chlamydia trachomatis was the causative pathogen in 109 patients, Trichomonas vaginalis in 52, Escherichia coli in 26, enterococci in 25, Proteus mirabilis in 14, Klebsiella pneumoniae in six, Streptococcus agalactiae in eight, Ureaplasma urealyticum in seven patients with chronic prostatitis. Other patients had a mixed infection.