This investigation focused on the relation between metabolic control of maternal diabetes in pregnancy and the health status of the fetus and newborn in the spontaneously diabetic BB rat. The basic hypothesis tested was that "tight" control of maternal diabetes before conception and during pregnancy should result in diminished fetal and neonatal morbidity and mortality. Behavioral teratologic tests were employed to evaluate the possible long-term effects of diabetes in pregnancy on postnatal development. The results demonstrated that approximation to glucose homeostasis in diabetic BB dams was associated with increased litter and fetal size, decreased perinatal mortality, and a significant reduction in the incidence of congenital malformation. Postnatal growth and neurologic function were also enhanced. These findings are supportive of efforts to initiate diabetic control prior to conception and especially during the critical period of fetal organogenesis during the first 8 weeks of human pregnancy.