Introduction: Normal human prostatic secretion is remarkably rich in citrate (EPS-citrate). Prostate inflammation will result in reduction of EPS-citrate level. So EPS-citrate was determined to investigate whether EPS-citrate level was also decreased in category IIIB prostatitis and whether it is feasible for EPS-citrate to be used as a diagnostic marker for category IIIB prostatitis. Materials and Methods: 21 category II outpatients, 25 category IIIA outpatients, 25 category IIIB outpatients and 21 normal controls without any prostatic diseases were included. All category II, IIIA and IIIB outpatients had not received any management. The EPS-citrate was determined by high-performance liquid chromatography. Results: The mean EPS-citrate values were 3.32 ± 0.79, 3.41 ± 0.88, 4.37 ± 0.77 and 8.55 ± 1.20 mg/ml in groups II, IIIA, IIIB and normal controls, respectively. Compared to normal controls, the EPS-citrate levels were significantly decreased in category II, IIIA and IIIB patients. Furthermore, there was no overlap of EPS-citrate values between category IIIA and IIIB patients and the normal control group. Conclusions: The EPS-citrate level is decreased in category IIIB prostatitis and it is feasible for EPS-citrate to be used as a useful diagnostic indicator for category IIIB prostatitis.