To evaluate hemoglobin AIc (Hb AIc) as an indicator of prolonged glucose control in pregnant diabetics, four groups of subjects were studied--16 pregnant diabetic, 13 pregnant nondiabetic, 12 nonpregnant diabetic, and 18 healthy control subjects. Hb AIc was significantly lower in the pregnant diabetic than in the nonpregnant diabetic subjects, 7.8% +/- 1.6 vs, 9.9% +/- 1.9 (mean +/- SD). No difference was present in the nondiabetic groups (4.0% +/- 0.7 vs. 4.3% +/- 0.8, respectively). Hb AIc correlated significantly with the average glucose concentrations of the preceding 60 days in both diabetic groups, suggesting that the lower concentration of Hb AIC in pregnant as compared with nonpregnant diabetic patients was because of better control of blood glucose. This was also borne out by the average of fasting glucose levels being 6.1 +/- 1.7 mmol/L in the pregnant diabetic and 10.7 +/- 2.2 mmol/l in the nonpregnant diabetic subjects.