1. Chronic dietary potassium depletion which was severe enough to decrease skeletal muscle intracellular potassium concentration by 20%, did not significantly reduce cardiac intracellular potassium concentration of rabbits.
2. Chronic potassium depletion caused a fall in intracellular pH in skeletal muscle, but no changes occurred in cardiac intracellular pH.
3. Intracellular potassium was increased above normal after 1 week of potassium repletion, but had returned to normal after 3 weeks of repletion. This may have resulted from potassium retaining mechanisms which had developed during depletion and which persisted during the early stages of repletion.
4. Cardiac and skeletal muscle from potassium-depleted animals did not show any structural damage when examined by light and electron microscopy.