The observation that several Mexican-American women were taking oral hypoglycaemic agents while pregnant led to a study to confirm reports of associations between these agents and congenital abnormalities. 20 non-insulin-dependent (NIDDM) pregnant diabetic women with exposure to oral hypoglycaemic drugs during embryogenesis and 40 pregnant NIDDM women matched for age, race, parity, weight, and glycaemic control but not exposed to oral hypoglycaemic drugs were followed up. 10 infants (50%) in the exposed group had congenital malformations, compared with only 6 (15%) in the control group (p less than 0.002). 5 (25%) infants in the exposed group had ear malformations, anomalies not commonly described in diabetic embryopathy. Hyperbilirubinemia (p less than 0.04), polycythaemia, and hyperviscosity requiring partial exchange transfusions (p less than 0.03) were commoner among babies in the exposed than in the control group. 3 babies in the exposed group but none in the comparison group had severe prolonged neonatal hypoglycaemia lasting 2, 4, and 7 days; 2 of the 3 had been exposed for 22 and 28 weeks during gestation, whereas the third had been exposed throughout the first trimester. Although exposure to oral hypoglycaemic drugs during fetal life seems to be associated with congenital malformations and neonatal hypoglycaemia, a large, prospective study is needed to exclude the confounding effect of maternal metabolic derangement secondary to diabetes.