Experimental allergic neuritis (EAN) in the peripheral nervous system, without involvement of the central nervous system, was produced in laboratory animals by the injection of a basic neuritogenic protein, P1L, purified from human peripheral nerves. The animals manifested a positive skin test with P1L, and their lymphocytes were found to be transformed in vitro in the presence of this protein several days before the appearance of the clinical signs. Passive transfer of the disease was performed with lymph node cells from donor guinea pigs immunized with P1L protein. EAN, the experimental model for the human disease Guillaain-Barré syndrome, was shown to be a transient disease and could be suppressed by the administration of hydrocortisone.