The primary objective of this investigation was to determine the relative contributions of contact velocity and compression to acute neurological deficits and gross histologic changes following either central or lateral cortical impact with systematic, independent variations of contact velocity and depth of deformation. To investigate the response to midline and lateral cortical impact, rats were injured, under anesthesia, at 1 of 18 different combinations of impact velocity and compression parameters. Following injury, neurological response and the contusional state of the brain was noted. For both studies, acute neurologic responses correlated better with velocity compression product (VC) than with either velocity or compression alone. At low contact velocity, functional impairment is best predicted by maximal compression. However, as velocity increases, injury severity becomes a function of (VC), demonstrating the rate sensitivity of brain tissue. The central and lateral impact data support the viscous response (VmaxCmax) as a biomechanical predictor of rat brain injury.