Abstract Objective To investigate leucocyte Na +/H + exchanger isoform 1 activity in postpartum pre-eclamptics. Design Exchanger isoform-1 activity and intracellular resting pH were established in leucocytes isolated from two study groups. Sample Leucocytes isolated from 10 women who had had pre-eclamptic pregnancies more than five months postpartum, and from 10 age-matched normotensive women who were more than five months postpartum. Setting Hypertension Clinic, Antenatal Assessment Area, Leicester Royal Infirmary. Methods A well validated technique involving flurometry using a pH sensitive dye (BCECF-AM) was performed to determine exchanger isoform-1 activity and intracellular pH. Determination of exchanger isoform-1 protein abundance was performed by western blotting. Exchanger isoform-3 protein abundance was examined to rule out the possibility of activity due to this particular isoform. Results Intracellular pH was significantly lower in the postpartum pre-eclamptic group (7.11 +/- 0.02), compared with the postpartum normotensive controls (7.33 +/- 0.04; P<0.001). Exchanger isoform-1 efflux rate (in mmol/L/minute) was significantly higher in the postpartum pre-eclamptic group (35.91 +/- 3.1), compared with the postpartum normotensives (23.94 +/- 2.0; P = 0.005). Exchanger isoform-1 protein density was established to be similar among the two subject groups. No exchanger isoform-3 protein was identified by western blotting. Conclusion Our results suggest that elevated exchanger isoform-1 activity is an important finding in women who have suffered from pre-eclampsia. This increased activity is not due to an increase in exchanger isoform-1 protein abundance or the presence of exchanger isoform-3.