DIFFUSE AXONAL INJURY (DAI) is a brain injury characterized by prolonged traumatic coma not due to mass lesions that has dysfunction or structural damage to brain axons. DAI can be produced by inertial loading of the head in a centroidal or non-centroidal manner. This paper compares the effect of varying the direction of head movement on the severity of DAI. Three groups of 13 monkeys are presented, each subjected to a single non-impact distributed inertial acceleration pulse with head motion constrained to a single plane. In groups 1 and 3, non-centroidal acceleration was produced in the sagittal (rotation about the y axis) and coronal (about the x axis) planes respectively, with the center of rotation in the lower cervical spine. Group 2 was subjected to centroidal acceleration in the horizontal plane (z axis). Deceleration pulse duration (6-8 msec), peak angular deceleration (1-2 × 105 rad/sec2) and angular velocity (475-510 rad/sec) were comparable in each group. Results show that traumatic coma is longest in group 3, shortest in group 1, with group 2 intermediate. The percent of animals still in coma at 1 hour was 0, 30 and 100 in groups 1, 2 and 3 respectively. Pathologic analysis of axonal damage showed a similar difference and was more prevalent and more widespread in group 3 than in group 2, with group 1 having the least damage. Axonal damage of mild, moderate and severe degree was present respectively in 56%, 0, 0 of group 1, 10%, 90%, 0 in group 2 and 0, 12%, 88% of group 3. Brain stem damage was seen almost exclusively in group 3.All differences were significant at the p<0.05 level. These findings demonstrate 1) that the direction of brain motion is important in the amount of axonal brain damage produced by inertial loading, 2) that lateral head motions are more injurious than horizontal or sagittal, 3) that pure centroidal acceleration can be produced experimentally.