The P0, P1, and P2 proteins were isolated from rabbit sciatic nerve and demonstrated to have molecular weights of 30,000, 18,200, and 12,000, respectively, by polyacrylamide disk gel electrophoresis in the presence of sodium dodecyl sulfate. The P1 protein characterized by peptide mapping, optical rotatory dispersion and encephalitogenic activity appears to be quite similar to the CNS myelin basic protein. The P2 protein is distinctly different from the P1 protein as characterized by peptide mapping and optical rotatory dispersion. It appears to have a distinct secondary structure, predominantly of beta-configuration. The P0 protein is distinctly different from either of the basic proteins, especially with respect to its marked insolubility in aqueous solutions. It contains more than 1.0 mole of hexosamine which is not present in either the P1 or P2 protein. Both the P0 and P2 proteins failed to produce any evidence of experimental allergic encephalomyelitis or neuritis when injected into guinea pigs or monkeys. In contrast, the P1 protein produces experimental allergic encephalomyelitis in both species.