The aim of this study was to estimate the prevalence of equine arteritis virus infections in horses in eastern Poland using the SN assay and the ELISA test. Sera of 442 horses were examined. In the SN assay, antibodies to EAV were detected in 185 samples with a titer range of 1:8 to 1:512. All sera samples examined by the SN test were analyzed again by the ELISA test. In this study positive reactions were observed for 136 out of 442 samples examined. Sera of 10 horses which were negative in the SN assay gave a positive reaction in ELISA. On the other hand, 59 sera negative in the ELISA test were positive in the SN assay with titers of 1:8 or higher. The ELISA test detected 49 seropositive animals less than the SN assay. Statistical analysis of the results of this study shows that the ELISA test, as compared with the SN assay, has a sensitivity of 68.1 % and specificity of 96.1%.