It has been well established that birth defects may be induced experimentally by heterologous antisera directed against certain tissue homogenates. The investigators are interested in the underlying mechanism whereby antibodies cause abnormal embryonic development. In order to clearly delineate the mechanism of teratogenesis rat kidney antigen(s) which elicits the production of teratogenic antibodies will be isolated and characterized by various physico-chemical means. The nature of the antigenic determinant(s) which is responsible for eliciting teratogenic antibodies will be defined. Specific antibodies will be isolated immunochemically and utilized to determine the precise localization of the antibodies by the immunoperoxidase technique at the light and electron microscopic levels.