IgM detection by enzyme-linked immunosorbent assay (ELISA) is the most used method of establishing a cytomegalovirus (CMV) infection during pregnancy. In this paper, we discuss the results obtained assaying 1,000 sera from pregnant women by two ELISA kits: a traditional indirect ELISA and a more recent IgM-capture ELISA. All the sera that gave a positive ELISA value with one or both kits were further tested by immunoblotting (IB) to establish which CMV polypeptides were detected by IgM antibodies. From the results obtained, IgM-capture ELISA seems less sensitive than indirect ELISA, but correlates better with serological evidence of active CMV infections as judged by typical IB profiles.