Subtotally 5/6 nephrectomized rats and sham-operated controls were fed a diet deficient in K. Subtotally nephrectomized animals had significantly less K in their muscles and a lower serum K than control animals; there appeared to be no difference in serum CO2 content in the 2 groups; subtotally nephrectomized rats showed more focal necrosis and f ibrosis of the myocardium than control animals on a low K diet.