In an experimental set-up including ten shoulder specimens, increments in the acromiohumeral distance (the subacromial space) were measured on an X-ray radioscope after the vertical stabilizing structures of the glenohumeral joint had been cut. It was found that when only the supraspinatus tendons were cut, the acromiohumeral space only increased by a few millimeters. When first the coracohumeral ligament and then the proximal one-third of the anterior capsule were cut, the acromiohumeral distance was doubled in each case. Distal subluxation did not occur when only the anterior capsule was cut. When the coracohumeral ligament was also cut, the acromiohumeral distance was more than doubled. It is concluded that the most important structures in the pathogenesis of distal subluxation are first the coracohumeral ligament and then the proximal part of the glenohumeral capsule.