Ten normal healthy male subjects between 20-30 years of age were initially examined at Delhi (200 m) and thereafter air-lifted to an altitude of 3,500 m. Excretion of sodium, potassium and chloride in urine and their plasma level were determined at sea level (SL) and daily at high altitude (HA) for 4 d. At HA, four subjects developed high-altitude pulmonary edema (HAPE), four remained normal, and two suffered from acute mountain sickness. The results on normals and HAPE are presented. There was increased excretion of potassium at HA in both groups resulting in reduction of plasma level. The sodium and chloride excretion was also increased in normals at HA irrespective of urine volume. In HAPE cases, the sodium and chloride excretion was related to urine output. With the retention of fluid, the excretion of these ions in urine was diminished without a parallel change in plasma levels.