Balances of N, Cl, Na and K and changes of the electrolyte content of skeletal muscle, kidney, heart muscle and liver were observed in K and protein-deficient rats upon supplementing the diet with K and/or protein. A redistribution of K within the body seemed to occur when the deficient diet was supplemented with protein. The rats exhibited an unsatisfactory N retention and a poor growth response, the plasma K concentration was reduced, there was a precipitous fall in skeletal muscle K, and there were reductions of the K in the kidneys, heart muscle and liver. The animals remained in negative K balance, but this was not great enough to account for the muscle K loss. Calculations based on the tissue K concentration and changes in tissue weights indicated a small gain of K by the kidneys and a significant gain by the liver. In its redistirubtion within the body, a fraction of K theoretically released from skeletal muscle remained unaccounted for.