Blood pressure and leucocyte sodium content were measured in black Jamaican patients with pre-eclampsia and pregnant controls. Similar measurements were made in a group of mothers who had pre-eclampsia 36-38 weeks previously and their controls. An increase in cell sodium accompanied the high blood pressure in patients with pre-eclampsia. There was also some elevation of both blood pressure and cell sodium in patients who had had pre-eclampsia 36-38 weeks previously. These findings suggest that disturbances of cellular electrolytes continue into the post-partum period. Changes in intracellular sodium may be important in the pathogenesis of pre-eclampsia as they parallel the increase in blood pressure levels.