To estimate the behaviour of the thorax of the human cadaver and Hybrid III a total of 33 belt impact tests were performed with the two surrogates. These tests have shown that the Hybrid III thorax is stiffer than that of the cadaver and that the internal thoracic deflection transducer may not necessarily record the maximum thoracic deflection. The belt load was lower value with the cadavers, which confirms the differences in stiffness. A belt force of 10 KN in the cadaver tests was associated with an average of 6 rib fractures. If we consider the relationship between the thoracic deflection and the number of rib fracture cadavers showing 5 or more rib fractures sustained an external thoracic deflection at least of 7.5 cm measured at the mid sternum.The analysis of V*C parameter indicates an average V*C value of 0.77 for 6 rib fractures, and the values of V*C measured on Hybrid III are sligthly lower than those of cadaver tests.