We have examined the relationships between maternal connective tissue disease (CTD), fetal and neonatal health, and the presence of specific autoantibodies: antinuclear antibodies (ANA), anti-Ro, antiLa, anti-Sm, anti-RNP, anti-DNA, and anticardiolipin (ACL) in 27 mothers with CTD (Group A), and 10 asymptomatic mothers of babies with complete congenital heart block (CCHB), or cardiac arrhythmias (Group B). Compared to 100 normal pregnant controls, autoantibodies were significantly more common in both Group A (96.3%, p less than 0.0005) and Group B (70%, p less than 0.0005), although the prevalence of autoantibodies in the Group A mothers having abnormal babies compared with those who had normal babies did not differ. Anti-La was present only in mothers with abnormal babies (7 of 17 compared to 0 of 10, p less than 0.025). Anti-La did not occur without anti-Ro, but anti-Ro occurred in 9 mothers without anti-La. Anti-Ro was present in the serum of all mothers of infants with CCHB and occurred alone in 3 of 4 instances. Titers of anti-Ro did not differ between abnormal and normal infants or their mothers. ACL occurred alone in the serum of 10 of 38 mothers, and was present in 7 mothers who had infants with cardiac abnormalities other than CCHB.