Considerable evidence for shared antigenic determinants between nervous elements and lymphocytes has accumulated. It has also been suggested that this cross-recognition may be involved in the pathogenesis of human neurological diseases such as myasthenia gravis and multiple sclerosis. We report here evidence that a marker for natural killer (NK) cells, anti-Leu-7 (HNK-1), specifically binds to components of human and rodent central nervous tissue as well as peripheral nervous tissue, especially to myelin sheaths. In contrast, another NK-cell marker (VEP13) did not react with nervous tissue. Since NK-cell function is impaired in a population of multiple sclerosis patients, the observed cross-reactivity indicates that autosensitization against myelin may simultaneously cause a defect of NK-cell function. Furthermore, the shared antigenic determinant may help to identify a hitherto undefined nervous tissue antigen and simultaneously increase the knowledge about the nature of NK-cell antigens.