The tolerance to abrupt linear deceleration (- Gx) and the subject response to a lap belt restraint system were investigated. Nineteen adult male baboons comprised the test pool. The effects of impacts of 8.6-40 g were studied, with nonsurvivability used as the index of tolerance.The results indicated that the tolerance to impact (LD50) approximated a 32 g sled deceleration. Lethality was presumed attributable to the secondary impact as the head contacted the floor of the sled. Predominant lethal injuries included avulsion of the atlanto-occipital articulation and dislocation fractures of the cervical vertebrae with resulting transection of the spinal cord.Excellent linear correlations were established between peak lap belt and seat pan forces versus maximum sled deceleration. Likewise, a linear relationship was found between peak head angular accelerations and maximum sled deceleration.