It was recently found that the “potassium‐sparing” diuretic triamterene, given prophylactically, increases tolerance to digitalis intoxication. This study demonstrated that triamterene is also of therapeutic value in dogs acutely intoxicated with ouabain. Not only was the digitalis‐induced myocardial potassium efflux reversed, but also the efflux of magnesium was reversed. In the doses employed the clinical benefit was definite but not always permanent. Triamterene also seemed to stop the ouabain‐induced hypementilation and retching. A significant technical problem was the poor solubility and relatively low pH of the drug for intravenous administration. Triamterene has theoretic advantages over intravenous potassium chloride, as it affects membrane Na‐K dependent ATPase and may favorably influence the Ki/Ko ratio. The implications in man are clear.