Ninety rats were followed for 1 year after suprarenalectomy and upon analysis were divided into 3 groups containing respectively 35, 46, and 19% of the total number: (1) died within 30 days after operation from acute and subacute insufficiency, usually before the 13th day; (2) survived suprarenalectomy for many months, but were chronically insufficient and suffered progressive emaciation resulting in marked or complete absence of fat, asthenia, and lowered resistance, leading sometimes to snuffles and skin infections. Most of the animals died within 7 months after operation, no gross accessory adrenal rests being found ai autopsy; (3) no demonstrable clinical effects; the animals were biologically normal in every respect, and large accessory cortical masses were always found at autopsy. When studied clinically for many months after suprarenalectomy, the seriousness of the operation in regard to the ultimate life of the animal becomes evident. Contrary to reports in the literature, it was found that fully 80% of rats die from effects of suprarenalectomy within 1 year after operation.