The effects on renal sodium excretion of giving lithium chloride (LiCl; 0.75 mmol per kg body mass) by gavage or intravenously were investigated. The experiments were carried out on Wistar-Kyoto (WKY) or spontaneously hypertensive (SHR) rats in metabolic cages. The rats had been on a low-salt diet for 4 days. Urine excretion of water, sodium and potassium was followed before and for 24 h after giving LiCl. An oral dose of LiCl evoked a more pronounced renal sodium excretion in either strain of rat as compared to that following intravenous administration, in agreement with previous observations of the effects of giving sodium chloride. Choline chloride (1.5 mmol per kg body mass) given by gavage to WKY rats or SHR evoked no change in the renal excretion of sodium. Based on the results of the present study and on observations reported in the literature, we propose that the intestinal tract contains a sodium "sensor", which upon activation releases a natriuretic factor to cause renal sodium excretion. The present results indicate that the proposed "sensor" is sensitive to lithium but not chloride ions.