High sodium loads were administered intravenously to a group of subjects whose blood pressures covered a wide range. Despite large individual variations, the water and sodium excretion of the group were found to be significantly and directly correlated with blood pressure. (and, presumably, sodium) was lower in the hypertensive group. Differences in dietary salt intake prior to the studies were assumed to be inconspicuous, but were not measured.The present experiments were designed to study over a wide pressure range the relationship of the blood pressure level to sodium clearance and excretion rates in response to a fixed sodium load. METHODS AND MATERIALSThe subjects for these studies consisted of 45 patients from the wards and outpatient department of the Evanston Hospital. The majority were suffering from some form of cardiovascular disease (table 1). The group included 14 patients with a history of chronic congestive failure, who were well controlled at the time of study.No dietary restrictions were imposed except that the subject was instructed to take nothing by mouth from the prior midnight until completion of the test. Upon reporting to the laboratory at 7:30 a.m., height and weight were measured and the surface area was calculated. The patient was placed at bed rest and catheterized. The bladder was drained, washed with two 10 cc. portions of sterile distilled water and blown out with two 20 cc. portions of air. The specimen and washings from this collection were discarded. The catheter was clamped and left in place.At the end of a 30 minute control period the urine was collected by the procedure outlined above, the volume measured and the specimen saved for analysis. During this period, control blood samples were taken.Following the control period, 100 cc. per square meter of body surface area of a 5 per cent sodium chloride solution were infused into an arm vein over a 25-minute interval. Urine collections were made at 30, 60, 90, 120 and 180 minutes, respectively from the time of the start of the infusion. Blood samples were taken at the end of the first period and at the midpoint of all succeeding periods.