A method of extending the results of experiments on concussion-producing head rotations on lower primate subjects to predict the rotations required to produce concussions in man is presented. A rational scheme of development of the overall investigation is outlined. Theoretical scaling factors are derived and discussed and the results of concussion-producing tests on the Rhesus monkey are presented in chart form. A chart of angular acceleration required to produce concussion in the Rhesus monkey indicates that an acceleration of 40,000 radians per second 2 will have a >99% probability of producing concussion. The scaling factors presented herein tentatively indicate that an acceleration of 7,500 radians per second 2 will have the same probability of producing concussion in man.