To further evaluate the role of growth hormone (GH) in the neonatal period, the effects of GH or insulin-like growth factor 1 (IGF-1) administration were studied in the neonatal GH-deficient rat. Groups of pups from newborn litters were randomized to receive twice daily subcutaneous injections of recombinant bovine growth hormone (bGH, 5 micrograms), recombinant human IGF-1 (10 micrograms) or saline from the second to twelfth day of life. The effects on growth parameters, serum IGF-1 concentration, body composition and hepatic GH receptor binding were assessed. bGH-treated animals showed increases in body weight gain (p = 0.01), serum IGF-1 (p < 0.01), carcass nitrogen (p < 0.001) and carcass water (p < 0.001) compared to IGF-1 or saline-treated animals. No differences in these parameters were noted between IGF-1 and saline-treated groups. bGH-treated animals showed a significantly lower hepatic GH receptor binding (p < 0.01) compared to the other two groups. The demonstration of anabolic responses to GH administration in the neonatal period has implications for the possible role of GH in fetal and neonatal growth.