Various modes of head support systems were studied in conjunction with optimum body containment by exposing guinea pigs to abrupt deceleration in the ± Gx orientations. Nonsurvivability and the incidence of cerebral hemorrhage were used as indexes of impact tolerance. The effects of impacts up to 600 G were studied at entrance velocities of 40, 60, and 80 ft/sec. The head support system evolved from a thin, flat pad of resilient foam to a contoured, nonresilient foam support. As the head support system improved there was a general increase in survivability and a decrease in the incidence of cerebral hemorrhage until high G levels were reached where no additional protection seemed achievable.