The changes in plasma renin activity (PRA) during short-term salt depletion (and peroral furosemide on the first day) and after bolus injection of propranolol were compared to the change during long-term treatment with diuretic and with propranolol in 19 patients with benign primary hypertension. A highly significant correlation was found between PRA on short-term and long-term salt depletion (r=0.02). A highly significant correlation was likewise found between initial PRA and decrement of PRA after bolus injection of or long-term treatment with propranolol. Only a weak inverse correlation was found between PRA reached during short-term salt depletion or long-term diuretic treatment and the fall in diastolic BP during long-term treatment (r=0.60). No significant correlation was found between decrease in PRA on propranolol (bolus/long-term) and diastolic BP reduction. It is concluded that the short-term PRA response to salt depletion and propranolol in the individual patient gives a good prediction of the PRA level on long-term diuretic or propranolol treatment, but is of no value in predicting the BP reduction during treatment.