Since the early trials of antihypertensive drug treatment, regression of electrocardiographic evidence of left ventricular hypertrophy has been demonstrated. The first multiclinic trial in which these effects were reported was the Veterans Administration trial. In this study the development of abnormal QRS voltage, S-T segment depression or T-wave flattening or inversion in the treated patients was only one-fourth that found in the control group. In those patients with electrocardiographic evidence of left ventricular hypertrophy prior to randomization, reversal of the abnormalities occurred two and a half times more frequently in the treated patients then in the control patients. Other controlled trials have shown similar results with antihypertensive treatment. It is concluded that following antihypertensive drug treatment the electrocardiographic evidence of left ventricular hypertrophy in hypertensive patients is markedly reduced. However, the electrocardiographic signs associated with coronary heart disease did not seem to be altered.