ABSTRACT: Maternal IgG antibodies in sera and placenta eluates were studied by a cellular enzyme-linked immunosorbent assay (CELISA) method. Antibodies were not detectable in any of the serum samples obtained before or after delivery from nine normal primigravid women. Antibody activity was, however, present in five of nine placental eluates and two of nine neonatal sera tested in CELISA. Lymphocytotoxic antibodies were not detected in any of the samples tested. These results support the concept that the absence of antibody activity in maternal sera may be caused by the immunosorbent effect of the placenta.