Persistent peptide antigens in MS CSF represent linear epitopes. Phage peptides selected by MS CSF IgG (two peptides from patients 1 and 3, and one from patient 2) were separated on gradient 4–12% SDS-polyacrylamide gels, blotted to PVDF membranes and probed with corresponding CSF obtained at two time intervals (CSF #1 and CSF #2), followed by HRP-conjugated anti-human IgG detection. Duplicate blots were probed with anti-pIII antibody to detect phage minor coat protein as positive controls. In each patient, phage peptides were recognized by the paired CSF, indicating that they represent linear epitopes. The anti-pIII antibody blots showed a 64-kDa band of phage minor coat protein with all phage peptides. Data represent at least three independent experiments.