Recent clinical experience has suggested that slight changes in the position of the arm may alter significantly the level of the arterial blood pressure. The technique of recording the arterial blood pressure used by us and others was, therefore, observed critically. It was found that meticulous care was usually given to the use of a standard cuff and stethoscope, the proper fitting of the cuff on the arm, the avoidance of deep breathing, recording the arterial pressure in the recumbent, sitting, and standing positions; however little attention was given to the position of the arm when the arterial blood pressure was being recorded. The position of the arm varied from being held out perpendicular to the shoulder joint at a 45-degree angle from the body; to being held at a 10-to-15-degree angle of abduction at the level of the heart with the forearm slightly flexed (as when the forearm rests