1. Peripheral blood lymphocytes were isolated at room temperature in a low sodium medium in 17 normotensive control subjects (NC) and 13 patients with essential hypertension (EHP).
2. Lymphocyte sodium content was not significantly different between NC and EHP (3.1 ± 0.5, n = 11, and 3.6 ± 0.5, n = 10, respectively; means ± sem).
3. The effect of frusemide on the ouabain-resistant rate constant of sodium efflux (KNao) from these lymphocytes into a sodium-free medium was measured.
4. The frusemide-sensitive efflux rate constant was 75 ± 5 μs (n = 17) in controls and significantly lower in EHP (32 ± 7 μs, n = 13, P<0.001).
5. In human lymphocytes there is a ouabain-resistant, frusemide-sensitive fraction of sodium efflux into a sodium-free medium; this fraction may be reasonably attributed to a sodium-potassium cotransport system. This sodium transport pathway seems to be reduced in lymphocytes from EHP.