The significance of antinuclear antibodies (ANA) was studied in 51 ANA-positive women who had had a total of 170 pregnancies. 60 ANA-negative age- and parity-matched women with a total of 142 pregnancies served as controls. The perinatal mortality rate in the ANA-positive group was 18.6% (8/43), while there were no perinatal deaths in the ANA-negative control group. All the perinatal losses were stillbirths. The rate of spontaneous abortions was low in both groups, 2.0 vs. 3.3%, respectively. The ANA titer, complement-fixing activity and antigenic specificity did not correlate with the outcome of the pregnancy. Two infants of the ANA-positive women (3.9%) had a congenital atrioventricular heart block. In both cases the ANA was of the complement-fixing type.