Two basic proteins, P1 of molecular weight 14,2000 and P2 of molecular weight 12,300, purified from bovine peripheral nerve, were assayed for biological activity. The P1 protein is an exclusively neuritogenic agent, capable of producing clinical signs of experimental allergic neuritis (EAN) and histological abnormalities in the peripheral nervous system (PNS) of guinea pigs and rabbits, without any changes in their central nervous system (CNS). P2 protein, like the CNS basic encephalitogenic protein (BE), has combined neuritogenic and encephalitogenic activities, therefore it induces in these animals neurological signs and pathological evidence of EAN, as well as histological characteristics of experimental allergic encephalomyelitis (EAE).