Hypertension and cardiac hypertrophy were produced in rats either by the application of a constricting ligature to one renal artery or by overdosage with desoxycorticosterone acetate. In a number of them the hypertension was abolished either by removal of the affected kidney or by removal of desoxycorticosterone acetate pellets. Animals which had developed marked hypertension also exhibited a significant degree of hypertrophy of the cardiac ventricles. Those which had had as severe a hypertension and for the same length of time, but in which the hypertension had been abolished for a period of time prior to sacrifice, were found to have only slight hypertrophy or none. Regression of cardiac size was most prompt in those animals in which the blood pressure returned to normal rapidly and less marked in those animals in which hypertension persisted for a time after the attempted "cure.".