1. Two women with severe hypokalaemic alkalosis were investigated by means of muscle biopsy before and at the end of 2 and 3 weeks respectively of intense therapy with potassium chloride.
2. The muscle biopsy material was analysed for water, electrolytes, adenine nucleotides, phosphocreatine, free creatine, pyruvate, lactate, glycogen and free amino acids. The extra- and intra-cellular distribution of water, electrolytes and amino acids was calculated by the chloride method.
3. Both patients showed a marked loss of intracellular potassium and an increase in intracellular sodium concentration. The muscle magnesium content was also slightly decreased. After repletion with potassium chloride, muscle sodium and potassium became normal.
4. The contents of creatine phosphate, ATP, ADP, AMP, lactate and pyruvate were within normal limits, but the phosphocreatine/total creatine ratio was reduced. After repletion, a small change in the apparent creatine—phosphokinase equilibrium had occurred, suggesting a minor increase in intracellular pH.
5. The concentrations of the basic amino acids, lysine, arginine and ornithine were increased far above normal. The intracellular accumulation of arginine was much higher than the increase in lysine concentration and the histidine concentration was normal. This differs from findings in potassium-depleted rats, where the intracellular lysine concentration is much higher than arginine concentration and histidine is high as well. After potassium repletion the intracellular concentration of ornithine, lysine and arginine became normal in one case and decreased considerably in the other. An increased intracellular concentration of glutamate and glutamine was also observed after potassium repletion.