['Antiphospholipid antibodies (aPL), especially against phosphatidylserine and cardiolipin, are associated with a variety of neurological disorders. While it is believed aPL react with endothelial cells to cause cerebral thrombosis, it is not known to what degree aPL react with neural tissue nor which particular aPL specificities may be more relevant. We investigated direct aPL reactivity with the central nervous system (CNS) using 3 monoclonal IgM aPL that differentiate between cardiolipin and phosphatidylserine dependent antigens.', 'Brain and spinal cord from normal cat Felis domesticus and brain from CD-1 mice were reacted with aPL using indirect immunoperoxidase techniques. Monoclonal aPL were reacted with whole brain myelin by dot immunoblots.', 'Monoclonal D11A4, reactive with cardiolipin and not phosphatidylserine (CL+/PS-), did not react with any portion of the tissue. Both monoclonal 3SB9b (CL-/PS+) and BA3B5C4 (CL+/PS+) reacted in feline and murine CNS. Both labeled myelinated fibers in grey and white matter of brain and spinal cord in an identical pattern with positive control antibody against myelin basic protein and reacted with whole human brain myelin by dot immunoblot. 3SB9b (CL-+PS+) additionally reacted with ependyma and epithelium of the choroid plexus.'] Do monoclonal antiphosphatidylserine antibodies react directly with feline and murine central nervous system?