Osteocalcin and PTH serum levels were measured in 41 insulin-dependent diabetic pregnant women through the three trimesters of pregnancy with a total of 106 determinations of osteocalcin and 137 of PTH. In parallel we quantified these parameters in 90 normal pregnant women throughout the three trimesters of pregnancy. In addition calcitriol, osteocalcin and PTH levels were quantified at delivery in 16 diabetic pregnant women and 16 normal pregnant women at delivery, in cord serum and in the infants during the first days of life. Non-pregnant women (n = 48) were the control group. In normal pregnant women PTH levels increased during the third trimester and total calcitriol increased at delivery. Osteocalcin levels decreased in the second trimester but returned to normal values during the third trimester of pregnancy. Diabetic pregnant women showed constant PTH levels throughout pregnancy. At delivery in diabetic pregnant women, total calcitriol levels increased to a smaller extent than in normal pregnant women. Osteocalcin concentrations in the second and third trimester of pregnancy were lower than in the non-pregnant group. Infants of diabetic mothers showed lower PTH and osteocalcin concentrations than infants of normal pregnant women, whereas their calcitriol levels were similar. These data indicate that diabetes decreases bone turnover during pregnancy in the mother and during the perinatal period in their offspring.