SummaryThe measurement of125I‐insulin binding to erythrocytes from 34 samples of cord blood (% B/T = 11.2 ± 3.8) showed statistically significant differences when compared to adult erythrocytes (% B/T = 6.6 ± 1.7). Preterm erythrocytes (% B/T = 14.7 ± 3.4) bound significantly more insulin when compared to term erythrocytes (% B/T = 10.1 ± 3.2). The negative correlation (r= −0.613;P= 0.001) between insulin binding and gestational age indicates that the trend during the final trimester of gestation is toward the lower binding observed for adult cells.The major differences in binding between adult and term cord blood erythrocytes may be primarily attributed to differences in the number of binding sites per cell. Additionally, there are small differences in both affinity and number of sites per cell in preterm as compared to term and adult erythrocytes.SpeculationThe mechanisms governing insulin release from the pancreas are not maturein utero.Insulin released directly into the circulation from the fetal pancreas may be bound to tissue receptors in relation to the affinity and concentration of specific surface receptors, thereby, providing direct control at the cellular level for rapidly growing fetal tissues. Erythrocyte receptors may serve to transport insulin for this purpose.