Chronic relapsing experimental allergic neuritis (crEAN) was induced by repeated transfers of P2-protein reactive T lymphocyte lines. Clinically, each intravenous transfer of P2-reactive T cells induced a relapse of the disease with weight loss and flaccid paresis of the hindlimbs followed by recovery. After multiple transfers, recovery from disease was incomplete, leading to increasing neurological deficit during the remissions. The pathology of the lesions during exacerbations was characterized by massive inflammation in the peripheral nervous system, associated with extensive endoneurial oedema, nerve fibre destruction and wallerian degeneration. Selective primary demyelination and remyelination was found in the minority of affected nerve fibres. No onion bulbs were present in chronic lesions. In the central nervous system partial degeneration of the posterior columns reflected the extent of wallerian degeneration in the peripheral nerves and spinal roots. In addition, during stages of active disease some T lymphocytes and upregulation of Ia antigen expression were found in the spinal cord.