The intracellular pH (pHi) of skeletal muscle, obtained by needle biopsy, was determined in 14 patients with chronic non-terminal renal acidosis and 6 normal subjects. Furthermore, the muscle composition in electrolytes and alkali-soluble protein nitrogen was analyzed. In patients with chronic renal acidosis the mean pHi value (6.88 ± 0.12) was not significantly different from that of the controls (6.92 ± 0.11). No correlation between intra- and extracellular pH values nor between pHi and plasma creatinine or cell sodium ion concentration was found. A significant direct linear relationship between pHi and potassium content in skeletal muscle was observed. These results suggest that potassium depletion is partly related to the increase in intracellular hydrogen ion concentratio