The usefulness of the released proteins (RPs) prepared in our laboratory from the strain Y. enterocolitica for the serological diagnosis of yersiniosis was estimated. Yersinia enterocolitica 0:8 was cultured under calcium deficient conditions and the virulence factors were isolated from the culture supernatant. The purified proteins were solubilized using sodium dodecyl sulfate. The results of ELISA using released proteins obtained in our laboratory as the antigen were compared to the results of commercial ELISA-Mikrogen and ELISA-Euroimmun. One hundred serum samples obtained from patients suspected in clinical investigations for jersiniosis were tested. Comparison of the frequency of detecting in particular ELISA antibodies to Yersinia showed a high (> 85%) agreement of the results in all of the immunoglobulin classes. The highest sensitivity (97.4%) and specificity (95.4%) was displayed by the ELISA with our antigen in relation to the ELISA-Mikrogen when determining antibodies of IgM class.