The compound is referred to herein as chlorothiazide or Diuril (4). Qualitatively, at equal dosages and under similar experimental conditions, chlorothiazide induces changes in elec-trolyte excretion that more nearly resem-ble those knownto be causedby the organomercurial diureticagents than the response generally considered to attend the administration of a carbonic anhydrase inhibitor. Under reasonably nor-mal conditions of acid-base balance, the effect of chlorothiazide is to increase the excretion of sodium and chloride pre-ponderantly. The excretion of potassium and bicarbonate is increased slightly, if at all. However, the effect of the drug on theratio of sodium to chloride excreted per unit time varies according to the state of electrolyte balance of the dog.