The relationship between maternal glucose levels and the concentration of glucose and insulin levels in human milk from diabetic women has not been elucidated. In addition, the rate of appearance of intravenously injected insulin to the change in concentration of insulin in maternal milk has not been studied. To study this relationship of glucose levels in serum to glucose levels in milk, maternal milk and glucose levels were measured in diabetic lactating women (n = 7) and nondiabetic lactating women (n = 10). In addition, the change in milk concentration of insulin was studied after an intravenous injection of insulin. The maternal whole blood glucose in the seven diabetic women was stabilized at a baseline blood glucose of approximately 100 mg/dl and then elevated with an infusion of intravenous glucose to a level of three times baseline (approximately 300 mg/dl for up to 2 hours). The plasma glucose was then lowered back to baseline with intravenous insulin over 20 minutes. The baseline serum insulin and glucose levels were compared to nonlactating women who donated serum to measure insulin levels in normal controls. Maternal milk glucose levels rise following an increase of plasma glucose levels with a lag time to the peak glucose level of 40-90 minutes, and return to baseline following the return of plasma glucose to baseline with a lag time of 120-150 minutes. Baseline milk insulin levels are elevated in hyperinsulinemic women and the levels of insulin in the milk will rise dramatically above baseline values after an intravenous injection of insulin with a lag time to the peak of concentration in milk of 60-80 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)