The influence of fetal glucose and amino acid supply on the regulation of fetal plasma IGF-I levels was investigated in fetuses from starved ewes. Paired maternal and fetal blood samples were taken during an initial 2-d control period, after 48 h of maternal starvation, during a 24-h fetal infusion of glucose (n= 6) or an amino acid mixture (Synthamin 17, n= 5) with continued starvation, and after 48 h of maternal refeeding. After 48 h of starvation, maternal and fetal plasma IGF-I, insulin, and blood glucose fell significantly in both groups compared with control values (IGF-I for glucose group: maternal,− 18.53±6.60; fetal,− 5.23±1.81 nmol/L; amino acid group: maternal,− 18.2±6.97, fetal,− 5.12±1.61 nmol/L; both p< 0.05). Fetal glucose but not mixed amino acid infusion raised fetal plasma IGF-I, insulin, and blood glucose to near control values (glucose group fetal IGF-I,− 1.77±1.98; amino acid group,− 5.93±2.22 nmol/L; both p< 0.05). Maternal plasma IGF-I remained depressed during glucose infusion (− 16.33±8.32 nmol/L), but continued to fall in the amino acid group (− 21.41±8.20 nmol/L, p< 0.05). After 48 h of maternal refeeding, all values had returned to near control values for both groups (glucose group IGF-I: maternal,− 5.2±3.86; fetal, 0.01±2.2 nmol/L; amino acid group: maternal,− 11.66±3.2; fetal,− 0.70±2.61 nmol/L). We conclude that in the ovine fetus glucose may have a more important role than amino acids in the regulation of fetal plasma IGF-I.