The homogenous antinuclear antibody was found in the sera of three pregnant women with systemic lupus erythematosus. This antinuclear antibody was found in the babies' sera at birth in titers similar to those in the maternal sera. In each case the antinuclear antibody was a 7.0S globulin. All three babies were healthy at birth, and none developed any evidence of lupus erythematosus. Serial studies showed that the half-life of the antinuclear antibodies was similar to that of tetanus antitoxin, which would not react with tissue antigens. This suggested that the antinuclear antibodies were not reacting with their antigen in vivo. Antinuclear antibody could not be detected in amniotic fluid, colostrum, or milk.