We have demonstrated that a brief compression lesion of the rat spinal cord produces axotomy with minimal necrosis or scarring and that axons grow into such a lesion along longitudinally oriented capillaries and similarly oriented cordons of ependymal cells and astrocytes. Inasmuch as extensive, oriented growth of axons into a spinal lesion is never seen after transection, concussion, or other models of spinal cord injury, this new surgical procedure appeared to be applicable to the in vivo testing of pharmacological agents designed to promote neuritic outgrowth. The spinal cord of anesthetized rats was crushed extradurally for 1 s with a smooth jeweler's forceps. After 2 days when edema had subsided, the animals were reoperated. The dura mater was opened, and a polyethylene tube was implanted so that one end was fastened over the injury site and the other end was exteriorized at the back of the neck. The lesion site was superfused with 0.1 ml of control or test solutions four times daily for 2 weeks and then the animals were anesthetized and killed by vascular perfusion with fixative. After decalcification, the vertebral column and spinal cord were embedded in paraffin and stained by several histologic procedures including the protargol silver impregnation method for nerve fibers. Treatment with triethanolamine and cytosine arabinoside, substances which promote neuritogenesis in cultured spinal ganglia of chick embryos, markedly stimulated the growth of axons into the lesion of the rat spinal cord. We conclude (i) that it is possible to pharmacologically enhance the intrinsic growth capacity of CNS neurons and (ii) that brief compression provides a type of injury that is well suited to the evaluation of treatments aimed at promoting axonal regeneration.