To determine whether anti-cardiolipin antibodies (ACA) are associated with multiple sclerosis (MS) or myasthenia gravis (MG), sera from 42 patients suffering from MS and from 21 patients with myasthenia were studied, using an enzyme-linked immunosorbent assay (ELISA). No significant difference in IgG or IgM immunoglobulin isotypes between the MS myasthenic patients and controls was found.