We studied oligoclonal IgG band patterns of individual unbound plaque extracts from seven autopsy MS brains by immunofixation after isoelectric focusing (IEF). The specimens showed 10 to 15 distant oligoclonal bands in pH region 7.0 to 9.3. Band profiles of different sections from the same MS brain were similar, implying that there is a common immunologic response. When residues from these brain sections, after thorough washing, were eluted at low pH, only three of seven showed low levels of IgG by enzyme-linked immunosorbent assay. When the IEF profiles of unbound arid bound IgG eluates from one brain were compared, two plaques showed similar profiles, whereas one had a different pattern. A plaque from two other brains showed band differences in the alkaline region of the gel. The data suggest that in some plaques there is a common immunologic response, but the response is different in others.