Long-term morphology of spastic or flaccid muscles in spinal cord-transected rabbits. Despite difficulty in long-term maintenance of spinalized rabbits, muscular pathologic changes in chronic spinalized rabbits could be observed for a period of four weeks. Rabbits were prepared by spinal cord transection at T10 (spastic paralysis) or by spinal cord removal below L7 (flaccid paralysis). Spastic preparations showed hind-limb spasticity and reflex incontinence one to two days after operation. Hypertrophic fibers began to appear in spastic muscles after two weeks. This hypertrophy, thought to be caused by phasic repetitive contraction, was verified by electron microscopy to be different from normal exercise hypertrophy. Flaccid preparations maintained hind-limb flaccidity and overflow incontinence. In flaccid muscle, marked muscle fiber necrosis indicated rapid atrophy. Spinal deformity and joint contracture inactivate spinalized rabbits, and cause pressure sores. However, feeding assistance and avoidance of complications make long-term maintenance possible. 