Chronic prostatitis syndrome (CPS) is a common urologic condition that many clinicians find difficult to diagnose and treat effectively. The information about the composition of the flora of the seminal fluid in healthy men and patients with CPS is limited. The aim of this study was to define the microbial communities present in the seminal fluid of healthy men and patients with CPS and at in vitro detection of decomplementary activity (DCA) phenotypes of isolates along with their comparison with isolates from patients with or without CPS. The bacteriological study was carried out to 48 healthy men and 60 men with CPS. Culture specimens were spread on various selective media. Bacterial DCA was tested by measuring the decrease in complement activity (CH(50)) under the influence of culture supernatants. The most common isolates in both groups were coryneforms, lactobacilli, coagulase-negative staphylococci, micrococci and streptococci. Enterobacteriaceae, enterococci and Staphylococcus aureus were isolated only from the CPS group. The organisms from seminal fluid of healthy men exerted DCA at 3.56 +/- 2.15; 2.47 +/- 1.23 and 4.36 +/- 2.2 anti-CH(50) for staphylococci, micrococci and diphtheroids respectively. The DCA of staphylococci, coryneforms, Enterobacteriaceae, enterococci and micrococci from CPS group were 12.8 +/- 2.1 (p < 0.05), 4.4 +/- 3.6 (p > 0.05), 16.8 +/- 2.1, 7.2 +/- 1.9 and 11.6 +/- 3.3 (p < 0.05) anti-CH(50) respectively. The data obtained in this study testify the microecological disorders in microbiota of seminal fluid in CPS.