1. The inter-relationships between plasma aldosterone, plasma renin activity, potassium excretion and plasma potassium were evaluated in subjects with normal and decreased glomerular filtration rate.
2. In seven studies of healthy control subjects and 12 studies of patients with renal disease, daily urine collections, plasma aldosterone and plasma renin activity were measured on a free diet for 5–10 days and subsequently during the addition of 50 mmol of potassium chloride daily for 5 days. Plasma aldosterone was also measured in 22 hospital patients with normal glomerular filtration rate and 24 patients with reduced glomerular filtration rate.
3. Plasma aldosterone was similar in base-line conditions in patients with or without renal disease and increased similarly during the administration of potassium chloride, suggesting that potassium excretion in patients with reduced glomerular filtration rate probably does not depend primarily upon increased aldosterone.
4. Plasma renin activity increased similarly in control subjects and patients with renal disease during the administration of 50 mmol of potassium chloride/day, but plasma renin activity did not increase when 100 mmol of potassium chloride/day was given to control subjects.
5. With the administration of 50 mmol of potassium chloride/day mean daily potassium excretion increased similarly in control subjects and patients with renal disease but plasma potassium increased significantly (4·7 to 5·4 mmol/l) only in patients with renal disease, suggesting that their uptake of potassium into cells was impaired.