1. Renal artery constriction and sham operation produced a temporary fall in the faecal sodium/potassium (Na/K) ratio of rats. When contralateral nephrectomy had been performed, the ratio rose to normal with the development of hypertension. With an intact opposite kidney the ratio remained low, but was elevated by spironolactone. With or without contralateral nephrectomy, the ratio was normal in chronically hypertensive animals (>28 days).
2. Balance studies showed sodium depletion in hypertensive rats with a normal kidney in situ. It is suggested that this stimulates aldosterone secretion and the faecal electrolyte changes.