Sled impact tests were conducted to simulate the motion of a standard size car at rest impacted from the rear by a second car of equal weight traveling at 32 mph. The test subjects were anthropomorphic dummies and unembalmed cadavers. They were seated in a bench seat (headrest in its lowest position) and were three-point belted. In one test mode the seatback was held rigid and in a second test mode the seatback rotated rearward in response to the test subject's impact loading. The major kinematic difference, in either test mode, between the dummies and cadavers was that the dummy head oscillated while the cadaver's head did not. Autopsies indicated that all three cadavers tested with a deflecting seatback suffered neck injuries reaching AIS 3 scale while two of three cadavers suffered similar injuries with a rigid seatback. The third cadaver tested with a rigid seatback had no injury.