It has been well established that heterologous antisera against whole rat kidney homogenate when injected into pregnant rats during the embryonic organogenetic period may induce abnormal embryonic development. Attempts were made to isolate the active components from soluble rat kidney extract by ammonium sulfate precipitation, anion-exchange chromatography, and concanavalin A-Sepharose 4B affinity chromatography. The glycoproteins isolated were capable of stimulating the production of potent rabbit antisera. When injected ip into the 9th day pregnant rats, these antisera induced embryonic death, congenital abnormalities, and fetal growth retardation. Eighty-four surviving fetuses were examined, all of them were malformed. The most frequently observed congenital defects were anophthalmia and microphthalmia. Attempts were made to analyze the glycoprotein fraction by discontinuous and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The results indicate that the glycoproteins were of high molecular weight and could be dissociated by SDS into a multitude of molecules or subunits. Although double immunodif-fusion indicated that there were one major and two minor antigens in the glycoprotein fraction, attempts to identify the antigens as to their size by analytical gel electrophoresis have not been successful. Electron microscopic study seemed to suggest that the glycoproteins might tend to aggregate to form particulates. The underlying mechanism whereby the antisera to these glycoproteins induce abnormal embryonic development is not understood. The hypotheses to explain the possible sites of teratogenic antibody interaction are discussed.SpeculationHeterologous antibodies are known to be transmitted from the mother to the fetus. The data indicate that the antigens which stimulate the production of teratogenic antibodies are glycoproteins. Recently, it has been demonstrated by other developmental biologists that each tissue contains a specific aggregation factor that ligates cells of that particular tissue. These aggregation factors are glycoproteins. It is possible that a population of heterologous antibodies directed against rat kidney glycoproteins may crossreact with some aggregation factors and, thus, interfere with cell-cell interaction at the time of histogenesis resulting in abnormal embryonic development.