Introduction: The objective of the study was to assess the relationship between Chlamydia trachomatis (C.t.) infection of the prostate and the concentration of citric acid. Materials and Methods: The study involved 60 patients with chronic prostatitis (NIH III). Urethral swabs and expressed prostatic secretions (EPS) were collected for analysis. The urethral swabs were tested for PMNs and the presence of Neisseria gonorrhoeae and C.t., while the EPS were analyzed to determine PMN count, C.t., and citric acid concentration. The DFA or LCR method was used for C.t. diagnosis. The concentration of citric acid was measured using the UV method. Results: Inflammation of the prostate (PMNs 10/field) was diagnosed in 58.3% of the patients. C.t. infection was found in 20%, including 8.3% with only the urethra affected and 10% with only the prostate. One patient had both the urethra and the prostate infected. A reduction in the concentration of citric acid in EPS was observed in 56.7% of the men. In 88.2% of the patients, reduced citric acid concentration was accompanied by an elevated PMN count in the EPS. All patients with C.t. infection of the prostate showed a reduced concentration of citric acid. In five patients with urethral infection, lack of a decrease in this parameter was noted in one. In all the patients with chlamydial infection, irrespective of localization, a high PMN count was observed in the EPS.Determination of the concentration of citric acid in the prostatic fluid is a good indicator of prostatitis. C.t. infection of the prostate gland is accompanied by a decrease in the concentration of citric acid.