An attempt to summarize and correlate the possible injurious mechanisms occurring in whiplash and head injury by impact is presented. The relation between whiplash and cerebral concussion has been investigated in two ways. First, it is demonstrated that a collar restricting bending and twisting but not stretching of the neck, as well as reducing rotational acceleration of the head, significantly raises the threshold for experimental cerebral concussion produced by occipital blows to the freely moveable head in monkeys. Secondly, experimental whiplash without head impact in the monkey can produce significant reduction of standard responses to external stimuli. It is suggested that multiple mechanisms are involved in cerebral concussion, among them rotational acceleration of the head, flexion-extension-tension of the neck and intracranial pressure gradients being probably the most significant. The direction of future investigation is indicated.