The avulsion of the brachial plexus in man results in paralysis of the affected upper extremity and often leads to severe, intractable and so far unexplainable pain. The consequential changes in the spinal cord immediately following the avulsion of the roots have rot yet been -totally ascertained. Inour work we aimed at examining the initial post-avulsion changes by developing a new model of avulsion of the brachial plexus in an experiment using rats. The obtained results could be useful for a better understanding ofthe clinical syndrome observed in man. The model was tested on 15 rats. Laminectomy and opening of the dura were performed, and the dorsal and ventralroots from the C5 to Tl levels on the left side were avulsed. Postoperatively, the ability of movement, response of the paws to pinching, and selfmutilation of the toes in the tested animals were followed. The rats were sacrificed at different times within 60 days after the procedure . The specimens taken at different levels of the spinal cord were examined by employing classical and special histological methods and immunohistochemical reactions. Verification of the results was carried out in the control group. Contrary to the assumption that the weakest site in the avulsion is at the attachment of the roots, our experiment has proven that there is a greater extent of the damage. The avulsed part of the spinal cord as a rule consisted of Lissauer s tract and a tip of the dorsal horn on the side of the lesion. Inthe region of the avulsed ventral root, laceration of the fibers and minor bleedings often occurred. The b1eedings, oedema and inflammatory reaction around both defects can explain the secondary damage of the spinal cord tissuewhich, in our experiment, was not equally extensive in each case .