The validity of reproduction of the controlled contusion injury to the spinal cord in the experimental animal is questioned. The dynamic pathology involving the microvasculature within the first two hours is illustrated using light microscopy. After 15-30 minutes swelling of axons and disruption of myelin sheaths become evident in most areas of white matter. After four hours microcysts have formed in the columns of white matter and are evidence of irreversible damage. Swelling of the cord following injury results from congestion, extravasation and intracellular swelling of neurones, rather than from any demonstrable increase in extracellular fluid. Oedema was only demonstrated with perfusion fixation. Isotope and contrast myelography were compared in the identification of the degree and extent of spinal cord swelling. Significant improvement in motor power was found in a group of paraplegic sheep treated with alpha-methyl paratyrosine. There was no significant improvement in the degree of recovery of motor power or sensation in those animals treated with intrathecal methyl prednisolone (Depo-Medrol). The histopathology in the crushed spinal cord tissue of the treated and untreated animals at various intervals of time was compared. Some possible explanations for the different patterns of clinical recovery in the treated animals are discussed.