DIAGNOSIS IN A DISCUSSION of the management of arterial hypertensive disease no topic is of greater importance than proper diagnosis. Despite the fact that we do not find distinguishing characteristics for most of our patients with hypertension, the considerable prognostic and at times therapeutic value of making an etiologic diagnosis renders careful diagnostic study highly desirable. This discussion is directed mainly toward treatment of those patients who have (1) so-called "essential" hypertension or (2) hypertension from known etiologic factors but whose elevated blood pressure fails to respond to causal therapy. We believe that in order to arrive at the correct diagnosis it is desirable to have a complete history and physical examination (including blood pressure in both arms and in one thigh), roentgenograms of the heart and lungs in three or four projections, a 12-lead electrocardiogram, estimation of basal blood pressure after heavy sedation, fractional phenolsulfonphthalein test, blood urea nitrogen