The response of plasma renin activity (PRA) to orally administered furosemide was determined in 100 unselected hypertensive patients. Twenty-six percent of the white patients and 51% of the Negro patients had suppressed PRA. Eighty-five percent of the patients with suppressed PRA after furosemide administration also had low renin levels on a low sodium diet. There was no correlation between the degree of natriuresis or diuresis following furosemide and the levels of PRA. The aldosterone excretion rate was elevated in only two out of 23 patients with suppressed PRA. Aldosterone-producing adenomas were present in each instance. Adrenal adenomas were removed in two other patients with hypokalemia and normal urinary aldosterone. Only one patient responded to surgery, although PRA returned to normal in both.