Essential hypertension is associated with insulin resistance and hyperinsulinemia. To assess whether hyperinsulinemia is also present in hypertensive disease induced by pregnancy, we studied the plasma glucose and insulin responses to 50 g of oral glucose in 10 women with definite, severe preeclampsia but normal glucose tolerance, and compared them with the responses observed in a well-matched control group of healthy pregnant women. Fasting plasma glucose concentrations were similar in healthy and preeclamptic pregnant mothers (4.1 +/- 0.4 mmol/L v 4.5 +/- 0.4 mmol/L, respectively, P = NS). Similar plasma glucose levels were also observed after glucose ingestion (5.5 +/- 0.3 mmol/L v 6.2 +/- 0.3 mmol/L in healthy and preeclamptic women, respectively P = NS). In contrast, fasting plasma insulin concentrations in the preeclamptic women were significantly higher than in normal pregnant mothers (175 +/- 29 pmol/L v 101 +/- 11 pmol/L, P < .05). Postload plasma insulin concentrations were nearly fourfold higher in the preeclamptic group as compared with the control group (1162 +/- 70 pmol/L v 366 +/- 39 pmol/L, P < .01). We conclude that preeclampsia is associated with marked hyperinsulinemia both in the fasting state and after oral glucose ingestion, suggesting that insulin resistance may play a role in pregnancy-induced hypertension.