Leucocyte sodium content and sodium pump activity was studied in overweight and lean hypertensive subjects and normotensive controls, all in the fasting state. In lean subjects (body mass index less than 27 kg m-2), hypertensives did not have altered leucocyte sodium content or pump activity. In the overweight (mostly obese) subjects, the leucocyte sodium content was higher in hypertensive than in normotensive subjects (median (range) 56.1 (42.0-84.1) vs 32.0 (18.2-59.4) mmol kg-1, P less than 0.001). This raised sodium content in overweight hypertensives was associated with a lower (ouabain-sensitive) 22Na efflux rate constant (2.25 (1.15-3.01) vs 2.64 (1.98-3.61) h-1, P less than 0.05) and a higher passive (or ouabain-insensitive) 22Na efflux rate constant (0.90(0.53-1.18) vs 0.63 (0.21-1.09) h-1, P less than 0.01). The systolic and diastolic blood pressures were significantly correlated to intracellular Na+ in the overweight group (r = 0.41 and 0.56, P less than 0.02 and 0.001 respectively). Thus, hypertension in the overweight subjects is associated with accumulation of intracellular sodium that may be due to abnormalities of the active sodium pump, though changes in ouabain-insensitive mechanisms also occur.