Estimates of splanchnic energy substrate exchange in the primate infant have been obtained using a baboon model. The splanchnic bed of the fasting baboon newborn released glucose at an estimated rate of 14.5 ± 5.0 µmol/min·kg body weight. Splanchnic glucose release in the fasting 5-7-wk old baboon infant proceeded similarly at an estimated rate of 15.5 ± 4.5 µmol/min·kg body weight. The principal precursors taken up by the splanchnic bed were lactate, glycerol, and alanine. Uptake of alanine correlated in a linear fashion with glucose release. Lactate was the most important precursor in both age groups. Glucose recycling through lactate is an active mechanism in the primate fetus as well as in the young of other species.