The intracellular electrolyte concentrations in skeletal muscle from 15 patients with ulcerative colitis or Crohn’s disease were examined. In patients with diarrhea not receiving potassium, muscle cell potassium and magnesium were low and sodium insignificantly elevated. By contrast, largely normal muscle cell electrolyte concentrations were found in patients receiving potassium or having a normal intestinal function. Supported by the existence of normal muscle cell electrolytes in a control group of patients receiving prednisone for extraintestinal diseases it was stated that glucocorticoid treatment does not affect the muscle cell electrolytes unless such treatment is effective in controlling the intestinal function. Potassium – and possibly magnesium – supplementations are recommended in cases with diarrhea.