There has been much dispute about the pathomechanics and the significance of the test even among the most competent surgeons in this field. Some have claimed that the posterolateral capsule must be torn to initiate the pivot shift. Some have even gone as far as to deny the importance of the anterior cruciate ligament as a main stabilizing structure of the knee. We evaluated the concept of MacIntosh in anatomical studies which were carried out at the both Pathology and Orthopedic department of Kyungpook National University, School of Medicine, Taegu Korea. Experiments have been carried out to study the etiology of anterolateral instability and the production of a pivot shift sign. In the cadaver knees and A/K amputation knees, which did not have any sign of instability or osteoarthritis, the anterior cruciate was severed by a short medial incision. We could immediately detect a pivot shift. No pivot shift resulted however when the posterolateral capsule was completely divided first and the anterior cruciate left intact, or when the medial collateral ligament and medial capsule were cut. If both the anterior cruciate and posterolateral capsule were divided the pivot shift became more prominent than after cutting the anterior cruciate alone. When the medial collateral ligament including the capsular structures was completely severed, however, the pivot shift disappeared. In summary the experiments show the following: 1. An isolated rupture of the anterior cruciate ligament or its combination with a partial tear of the medial collateral ligament may be detected with the pivot shift sign. 2. If the rupture of the medial collateral ligament is complete the pivot shift test can be negative in spite of a tear of the anterior cruciate ligament.