ABSTRACTWith the macrophage electrophoretic mobility (MEM) test of Field&Caspary, Iymphocyte sensitization to thyroid antigen (F1‐fraction) is demonstrable in all subjects‐multiple sclerosis (MS) patients, those with other (destructive) neurological diseases (OND) and normals. the MEM‐LAD test enables a further differentiation to be made in neurological patients compared to normals: Linoleic acid inhibits the positive result by about 95 per cent in the case of MS, 58 per cent in normals and 45 per cent in OND. the high reduction appears to be a characteristic of MS. It is seen at all stages and in all forms of the disease and is not materially influenced by moderate immunosuppressive therapy. the mothers of MS patients show an intermediate result of about 78 per cent, suggesting a familial (genetic) background to the metabolic phenomenon described here; there is, however, evidence of an added exogenic factor for the development of the disease. the theoretical basis of the LAD test suggests further therapeutic trials of linoleic acid in treatment