Rats show increased consumption of sodium-containing solutions following the administration of mineralocorticoids. This increased consumption has been termed sodium appetite. In the present experiment, the administration of various doses of aldosterone led to increased intake of a 0.33M saline solution in both domestic and wild rats relative to the appropriate control groups. Both plasma sodium and plasma volume increased slightly following the administration of the hormone. However, rats raised with a saline solution continuously accessible on their cages from birth did not show sodium appetite following the administration of aldosterone unless some minimal period of time had elapsed wherein they had received no saline at all. These data, along with the data of several control experiments, imply that aldosteroneelicited sodium appetite is the result of some learning process. One hypothesis is that, during their development, an association forms in rats between increased aldosterone levels and the tendency to consume sodium when body sodium levels are relatively decreased. Later, the presence of increased aldosterone elicits sodium appetite in the absence of a low body sodium. (Endocrinology89: 538, 1971)