Using the sodium sulfate precipitation radioimmunoassay and solid-phase radioimmunoassay, we measured antibody to intact human myelin basic protein and myelin basic protein peptic fragments, residues 1-44, 45-89, and 90-170, in CSF. Comparable levels of binding were obtained for MS and normal CSF by both tests. The increased amount of CSF IgG in MS patients cannot be attributed to specific antibody against myelin basic protein or its peptic fragments.