The influence of alterations of adrenal function upon the responsiveness of the rat to intravenously administered ouabain was studied electrocardiographically by the string galvanometer. Conduction disturbances followed by cardiac arrest were the criteria for a definitive response. Adrenalectomized rats showed a significant increase in sensitivity to ouabain as compared with normal controls. Normal animals implanted with pellets of desoxycorticosterone acetate and continuously maintained on saline drinking water did not show a significant alteration in their responsiveness to ouabain.