Spontaneously hypertensive (Okamoto-Aoki) rats (SHR) and normotensive (Wistar-Kyoto) rats (WKY) were fed a regular or a high fat diet when they were weaned; animals from each group were autopsied at 60, 90, 230, 250, and 180 days of age. SHR fed the high fat diet were cachectic, their pituitary glands were abnormally small, and despite severe hyperlipidemia, hyperglycemia, and adequate corticosterone levels, their zona glomerulosae were completely depleted of lipid, and they did not develop hypertension (110-115 mm Hg) or any manifestation of atheromatous changes. WKY fed the high fat diet became obese, their pituitary glands increased in size, and their normal blood pressure was slightly reduced (90-115 mm Hg). SHR fed the regular diet developed their usual severely elevated hypertension (185-205 mm Hg). It is suggested that the introduction of a high fat diet at an early age will cause hypopituitarism and inhibit the spontaneously appearing hypertension in SHR.