The Korotkov compression sounds, obtained by means of sound capsules from normal men and patients with aortic regurgitation, consist of 3-6 regular vibrations occurring at a frequency of 40-256 v. d. per sec., and lasting 0.041-0.1275 sec. Each sound can be divided into preliminary, main and final vibrations. During progressive decompression the pitch of the sounds tends to fall as their intensity increases. The loudest sounds have comparatively low pitch and long duration. Murmurs of appreciable magnitude and duration rarely occur provided a cuff of proper width is employed. Reduplication is occasionally encountered. The Korotkov sounds begin earlier with respect to the initial rise of the compression pulse as the pressure is lowered, indicating an earlier penetration of the compressed artery by the blood jet. The work supports the water hammer theory suggested by Erlanger as explanation of arterial sounds in animals. The general similarity of the vibrations at all levels of pressure indicates origin at one fixed point. Eddies and whorls do not contribute. The division of the Korotkov sound into so-called "phases" is unwarranted.