The etiology of prostatitis is not fully understood and several causative factors have been considered in the past. In this study we analyzed the expressed prostatic secretion (EPS) and seminal plasma with regard to uridine, xanthine, urate, creatinine and zinc from patients with prostatitis (the diagnosis was based on symptoms for at least 1 year), together with creatinine, urate and zinc in the serum. In 8 of the patients, a direct comparison of these constituents was performed between EPS and seminal plasma. EPS contained low concentrations of uridine and xanthine and high concentrations of creatinine and zinc as opposed to seminal plasma that displayed a reverse pattern. The mean urate concentration in seminal plasma, exceeding that of EPS by 78%, was rather close to the mean value found in serum but no significant correlation was seen between urate in serum and urate in seminal plasma or EPS. Urate in EPS correlated significantly to xanthine in EPS and such a relationship was also observed between urate and creatinine in EPS. In seminal plasma, urate and xanthine were likewise correlated with each other. On division of the patients into a high-score symptom group and a low-score group, no intergroup differences were found in EPS and seminal plasma constituents. Hence, we found high concentrations especially of uridine and xanthine in seminal plasma, compared with other body fluids, and evidence of a backflow of urine mixing with the prostatic fluid of these patients was seen. We suggest that crystal formation of these metabolites may occur under certain conditions and could constitute a first step in the development of prostatitis-vesiculitis-epididymitis in some cases.