Peritoneal dialysis (PD) does not demand special equipment and its fluid composition can be easily changed according to the individual condition. Nine patients with chronic or acute renal failure presented severe metabolic alkalosis (MA). Hemodialysis (HD) proved virtually ineffective and the MA persisted. Physiological saline solution was adopted as the main component of the PD fluid for the treatment of MA. By this method, Cl- can be shifted from PD fluid to extracellular fluid (ECF) and HCO3- from ECF to PD fluid by ionic gradient. Therefore, pH and base excess (BE) of these patients both improved to the normal range after several fluid exchanges. The lowering effect of BE (delta BE/L) ranged from 0.99 to 2.6. Hyposaline and normo-osmol solution (Na+ 70 mEq/L) were used for one patient with hypernatremia and consciousness disturbance. Serum (S)-Na decreased from 170 to 138 mEq/L, and consciousness became almost clear with the use of 15 L of PD fluid. Hypersaline solution (Na+ 190 mEq/L) was used for two patients with hyponatremia (S-Na 113 and 121 mEq/L). S-Na rose to within the normal range after 16 and 9 L in the two cases. A fluid mixed with distilled water, 10% NaCl and 7% NaHCO3 (HCO3 34-68 mEq/L) was used to treat lactic acidosis in two patients. By this method, HCO3- can be shifted from PD fluid to ECF and lactic acid from ECF to PD fluid. Two patients recovered from prolonged shock, and pH was corrected by 10 L and 4 L, respectively. PD should be considered for application in other diseases besides renal failure.