Knowledge of altered maternal nutrition effects on growth-regulating systems is critical to understanding normal and abnormal fetal development. There are many reports of hepatic fetal IGF system responses to maternal nutrient restriction (MNR) during pregnancy in rodents and sheep but none in nonhuman primates. We determined effects of MNR on the fetal baboon hepatic IGF system. Social groups of female baboons were fed ad libitum, controls, or 70% controls (MNR) from 0.16 to 0.5 gestation and fetuses delivered by cesarean section. Fetal liver tissue was analyzed for IGF-I, IGF-II, and IGF binding protein (IGFBP)-3 mRNA by in situ hybridization and quantitative RT-PCR and protein by immunohistochemistry (IHC); IGF-I receptor, IGF-II receptor by quantitative RT-PCR and IHC and IGFBP-1 by in situ hybridization and IHC. MNR did not alter fetal body or liver weight. Fetal hepatic glycogen staining increased with MNR. MNR reduced fetal hepatic IGF-I and IGF-II and increased IGFBP-1 mRNA and decreased IGF-I, IGF-II, IGF-I receptor, and IGF-II receptor protein and increased protein for IGFBP-1 and IGFBP-3. MNR increased caspase-3, indicating apoptosis and decreased Akt staining, indicating decreased nutrient sensing. In conclusion, whereas fetal body and liver weights did not change in response to moderate MNR during the first half of baboon pregnancy, the major indices of function of the hepatic IGF system measured were all reduced.