The present study was performed with the objective to investigate the possible effects of recombinant human growth hormone (rhGH) supplementation on protein and glucose metabolism during the early postnatal period in seven intrauterine growth-retarded (IUGR) preterm infants. Eight infants were studied as controls. The metabolic rate was measured by indirect calorimetry, and whole body protein and glucose kinetics were measured using constant-rate infusions of [1-13C] leucine and [U-13C]glucose during continuous adequate oral feeding. Energy expenditure was similar in both groups. In the rhGH-treated group of infants, leucine turnover (470 +/- 76 vs. 409 +/- micromol/ kg/day), leucine used for protein synthesis (402 +/- 72 vs. 337 +/- 36 micromol /kg/day), and leucine derived from protein breakdown (365 +/- 71 vs. 304 +/- 41 micromol/kg/day) were increased. However, net leucine balance was not increased (37 +/- 17 vs. 34 +/- 13 micromol/kg/day). The total rate of appearance of glucose was 10.1 +/- 1.2 vs. 10.0 +/- 1.3 mg/kg/min. We suggest that immediate postnatal treatment with rhGH is not effective in stimulating protein gain and has no effect on glucose kinetics in IUGR preterm infants.