Dietary restriction of rats during the suckling period is known to result in irreversible growth stunting, which cannot be corrected even by ample supply of food after weaning. In order to determine whether growth hormone (GH) deficiency might play a role in this permanent growth failure, circulating GH concentrations were assayed in postnatally malnourished rats following 10 days of nutritional rehabilitation. The significantly lower plasma GH values observed in the restricted animals as compared to a control group suggests a causal relationship between GH deficiency and the persistent retarding effect of the early nutritional insult. The experimental model employed in this study closely resembles human infantile marasmus. However, the regulation of GH secretion in the rat differs from that seen in primate species. Therefore, extrapolation of these findings to marasmic infants cannot be made without reservation.