Nutritional status in neonatal rats was manipulated by altering the litter size to produce overnourished (5-6 pups/litter) and undernourished animals (16-17 pups/litter) for comparison with standard nutritive status (10-11 pups/litter). Nutritionally deprived pups showed impaired body and cardiac growth and a slowing of development of cardiac membrane binding sites for alpha 1- and beta-receptor ligands. Overnourishment enhanced growth and receptor development. In all cases, restitution of receptor binding characteristics to normal occurred at the beginning of nutritional rehabilitation (i.e., at weaning), well before the return of body and organ weights. These results thus suggest that the ontogenetic pattern of receptor binding sites is dependent upon nutritional intake rather than on weight gains per se. Receptor deficits caused by neonatal malnutrition probably contribute to reduced responsiveness to adrenergic stimulation.