An electroimmunoblotting technique was used with a monoclonal antibody to myelin basic protein (MBP) to assess demyelination in 3 defined regions of the spinal cord in rats with acute experimental autoimmune encephalomyelitis (EAE). A slight loss in MBP was detected only in the sacrococcygeal region of the spinal cord after the onset of clinical signs. In all 3 spinal cord regions studied, significantly elevated levels of albumin and IgG were detected during the course of EAE by the same technique. At the onset of clinical signs, the levels of IgG and albumin were highest in the more caudal regions of the spinal cord. As the clinical signs became more severe, IgG and albumin levels increased in the more cranial regions of the spinal cord. These changes thus correlated with the ascending progression of clinical signs typical of EAE in rats. These results provided added evidence that in rats affected with acute EAE, the clinical signs occur independently of demyelination and coincide with vasogenic edema.