The venous plasma insulin and glucose concentration was investigated in 15 diabetic and 13 non-diabetic women at birth; in the umbilical cord blood of their infants at birth; 1.5 to 6 hours after birth in the fasting state; and 5 and 30 minutes after a glucose load injected through a catheter inserted in the umbilical vein. Insulin antibodies were estimated at birth. Antibodies were found in the maternal and the umbilical cord blood in 13 diabetic mothers who had had insulin treatment for 2–20 years, but not in 2 diabetics with, respectively, no insulin treatment, and treatment for a few days only. In infants of non-diabetic mothers, the insulin concentration at birth was lower than that of their mothers. In infants of diabetic women the insulin concentration was much higher than that of the control infants. After glucose injection a rapid increase of the insulin concentration in the umbilical vein was demonstrated in infants of diabetic women, whereas the rise was slow in infants of non-diabetics, thus indicating a greater reactivity of insulin secretion or release in infants of diabetic women. After glucose injection, the plasma glucose concentration in the umbilical vein rose and fell rapidly without any difference being found between the two groups, in contrast to the great differences in their insulin concentration.