CSF Ig from 28 patients with MS and 25 patients with other neurologic diseases (OND) were examined for their capacity to bind to rat or human oligodendrocytes in culture. We have used a double-label approach combining CSF Ig with antibodies against galactocerebroside (GalC). As normal human IgG at a concentration higher than 250 micrograms/ml were found to bind nonspecifically to oligodendrocytes in culture, patients' CSFs were used unconcentrated, at a final IgG concentration never exceeding 115 micrograms/ml. In these experimental conditions, we have not been able to detect any fixation of CSF Ig from MS (or OND) patients to rat or human GalC+ oligodendrocytes.