The relationships between serum potassium and urinary excretion of potassium and blood pressure were determined in an unmedicated adult population with a wide range of blood pressure (mean arterial blood pressure 100-130 mm Hg, n = 71). Inverse correlations between both serum potassium concentration and urinary excretion of potassium and standing (but not supine) mean blood pressure were seen (r = -0.41, p less than 0.005 and r = -0.33, p less than 0.01 respectively). These relationships persisted also when the influences of age, sex, obesity and kidney function were taken into account in a multiple regression analysis. The present observation is in accordance with previous reports of an association between potassium metabolism and blood pressure.