A test program has been conducted to determine the fracture behavior of the human frontal bone against two different rigid cylindrical surfaces; one surface was of 1 in. radius and one was of 5/16 in. radius; both were 6½ in. long. The purpose of this research program was to provide human tolerance data which would: 1. Assist in the design of structures likely to be impacted by the human head. 2. Extend the calibration range of frangible headforms. Twelve cadavers were tested in this program; seven against the 1 in. radius cylinder and five against the 5/16 in. radius cylinder. The test arrangement employed a guided drop of the test surface against a stationary head which was free to rebound. Drop heights were increased progressively until borderline fractures were obtained.The large radius shape consistently yielded linear fractures indicating that it is effectively a blunt surface. Fracture loads ranged 950-1650 lb. The small radius shape yielded two linear fractures and three localized elliptical fractures indicating that it is in the transition range between a blunt and concentrated surface. Fracture loads ranged 700-1600 lb.