One hundred sixty-three patients with graded degrees of uncomplicated stable chronic renal failure were studied to investigate the quantitative relationship between serum acid-base and electrolyte composition and serum creatinine level. Even in patients with a mild degree of renal failure, the serum total carbon dioxide (tCO₂) content was reduced significantly. Progressive decrements in tCO₂ were noted in the more severe degrees of renal failure with the reciprocal relationship between tCO₂ and serum creatinine concentration. Depending upon the degree of chronic renal failure, the type of metabolic acidosis was different. In patients with a moderate degree of renal failure, hyperchloremic acidosis was noted with anion gap remaining normal. As the renal failure progressed to a more severe degree, this pattern of hyperchloremic acidosis changed to anion gap acidosis with a normal serum chloride level. The highest anion gap was 25 mEq/L in the patient with serum creatinine concentration 24.7mg/dL.