Although perinuclear anti-neutrophil cytoplasmic antibodies (pANCA) are associated with vasculitic neuropathy, their association with central nervous system (CNS) disorders has not been studied except for one report on optic-spinal type of multiple sclerosis associated with serum pANCA. We examined pANCA in sera from 98 patients with various CNS disorders, such as 58 MS, 17 myelitis, 12 HTLV-1 associated myelopathy, and 11 other CNS diseases using indirect immunofluorescence methods. The results showed serum pANCA to be positive in five patients with a peculiar type of myelitis, including two with MS and three with etiology unknown myelitis. All of these ANCA-positive patients were women and had acute or subacute myelopathy with various severities. MRI revealed segmental swelling of the spinal cord with T2 hyperintensity in the acute stage of the disease. Marked pleocytosis (227.8+/-101/mm3) and elevated protein level (128.8+/-52 mg/dl) in CSF were noted. Four of the patients had anti-nuclear antibodies and two had previous histories of symptoms suggesting autoimmune disorders. In a search for target antigens of pANCA, myeloperoxidase reactivity was found in the sera from two myelitis patients. Clinical and laboratory features of myelitis patients with pANCA in the present study are different from those of typical MS patients. Further study will be needed to delineate the role of pANCA in the pathogenesis of a specific type of myelitis.