1. Leucocyte electrolytes were measured in pre-eclampsia and comparison was made with leucocytes from normal primigravidae and from the original pre-eclamptic subjects 6 months after delivery when blood pressure had returned to normal.
2. In pre-eclamptic subjects, leucocyte sodium was elevated and potassium depressed, and the rate constant for sodium efflux was depressed.
3. These changes returned to normal after delivery.
4. An increase in cellular sodium as a result of altered sodium pump activity may be the cause of hypertension in pre-eclampsia.