I . Metabolic alterations related to protein catabolism were studied in rats in transitional states induced by changing from a low-protein (LP) (so g caseinlkg) diet to a high-protein (HP) (250 g casein/kg) diet. 2. Twenty-four hours after the diet was changed, the rats showed a more rapid increase in live-weight gain than controls that had been fed on the HP diet throughout. On the 5th day after the diet change, their increase in body-weight had returned almost to the control rate. Food and

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... refore nitrogen intakes on the 1st and j t h days after the change in diet were the same as those of the controls. It seems likely therefore that the initial high rate of live-weight gain is an indication of a metabolic adaptation which occurred on the LP diet and which did not fully return to normal until the 5th day after the change of diet, +.