Experimental intrauterine growth retardation was produced in two groups of neonatal rats by maternal dietary restriction (DR) or by bilateral ligation of the uterine vessels (UVL). Both experimental groups of neonates had lower plasma glucose levels than controls at delivery. Newborns of DR animals showed appropriate suppression of insulin release and rapid recovery from hypoglycemia during an 8-hour fast. In contrast, neonates in the UVL group displayed persistently lower plasma glucose levels and inappropriate hyperinsulinemia. The metabolic effects of these two models of intrauterine growth retardation reflect the nature of the fetal insult and are not uniform.