Fifty-four children aged 10-15 years were studied. Twenty-two children had mothers who had sustained hypertension after a hypertensive pregnancy (HT) and 17 had normotensive mothers who had previously had a hypertensive pregnancy (NT). A control group consisted of 15 children with normotensive mothers (C). Blood pressure was significantly higher in the HT group in comparison with the C group (P less than 0.01). Erythrocyte sodium (Na+) and potassium (K+) concentrations were similar in all groups and not related to blood pressure. The Na+K+ATPase activity in erythrocyte membranes was lower in the HT group than in the NT group (P less than 0.02), but not significantly different from the C group. There was no statistically significant correlation between Na+K+ATPase activity and blood pressure.