Prevalence of seroimmunity to cytomegalovirus (CMV) infection was tested by detecting ELISA IgG antibodies in 230 pregnant subjects from low socioeconomic backgrounds. Seroimmunity increased from 64.3% to 92.0% between the ages 15-20 and 35-40. Furthermore, ELISA IgM antibodies were detected during hospitalization in a group of 56 women whose pregnancies ended in spontaneous abortion and in a paired matched-control group. The overall percentage of IgM-positive reactions was 5.35% in the group with abortion. The percentage for only second trimester abortions amounted to 18.75%. There was no IgM-positive reaction in the control group.