The effect of eight hours water diuresis on electrolyte excretion and urinary acidification was studied in five permanent inhabitants of a hot region. The experimental design excluded the possible influences of the normal diurnal variations on electrolyte and hydrogen ion excretion. Water diuresis induced a marked increase in ammonia output and decrease in potassium excretion. A significant (p < 0.001) inverse relationship is demonstrated between the net hydrogen ion excretion and potassium output. Glomerular filtration rate, total solute, sodium, chloride, calcium, magnesium, and titratable acid excretion were not appreciably affected. The data presented demonstrate that prolonged water diuresis in permanent inhabitants of a hot region did not appreciably alter the excretion of electrolytes except for a significant fall in potassium output. Its effect on urinary acidification was similar to that previously reported during short term water diuresis.