In the Lewis rat immunisation with the myelin P0 glycoprotein can induce an inflammatory demyelinating disease of the peripheral nervous system, experimental allergic neuritis (EAN), which has many clinical and histopathological parallels with the human disease the Guillain-Barre syndrome. In view of the reported association of GBS with a number of infectious agents we have investigated whether "molecular mimicry" may occur between microbial antigens and the P0 protein that could possibly trigger a similar pathogenic autoimmune response in man. A computer search of the available protein sequence data bases identified several absolute sequence homologies between P0 and viral proteins that involve five or more consecutive amino acid residues. Four of these sequence homologies involved viral pathogens previously associated with the Guillain-Barre syndrome, namely Epstein-Barr virus (EBV), cytomegalovirus (CMV), Varicella zoster virus (VZV) and human immunodeficiency virus I (HIV I). Although, sequence homologies were also found between viral peptides and the neuritogenic determinants of P0, residues 56-71 and 180-199, these homologies proved incapable of eliciting EAN in the Lewis rat. These observations are discussed with reference to the role that molecular mimicry between T cell epitopes on pathogen derived antigens and the P0 protein may play in the pathogenesis of the Guillain-Barre syndrome.