There are two general categories (not necessarily mutually exclusive) of congenital defects: (1) abnormalities that have an hereditary basis, such as single and multiple genes, or chromosomal abberration; and (2) abnormalities that are caused by nonhereditary factors, such as malnutrition, maternal disease, radiation, infections, drugs, or environmental chemicals. Research on congenital defects needs strong basic approaches that examine several levels of biologic organization, including cell differentiation, cell interaction, and defects at the genetic level. These approaches should be applied to specific clinical entities, such as developmental defects in human organ systems, family studies, and population genetics. Research emphasis should be focused on delayed, long-term effects that may be manifested long after birth. This monograph presents a report on current research progress in studies of congenital defects of gametes, the embryo, and the fetus. Included is an examination of prenatal exposure to toxic agents, such as drugs, industrial chemicals, pesticides, herbicides, fungicides, fertilizers, radiation, and viruses. Research findings and needs are cited for studies on: (1) recombinant DNA; (2) communication within the nucleus; (3) connective tissues; (4) cell adhesion, migration, and morphogenetic movements; (5) anencephaly and spina bifida; and (6) nonclonal antibodies. Priorities and recommendations for future research are listed. A bibliography of 162 references is included in the report. (JD)