"Adoptive mev" chimeras were created by grafting hematopoietic cells (HC) from B6 viable motheaten (mev) mice into bg or wild sublethally irradiated (SI) mice: the chimeras developed mev-type symptoms such as paw inflammation and necrosis, lung damage, thymus atrophy, and high serological IgM concentration and autoantibody levels as well as rapid death. The phenotype of adoptive mev mice could be obtained even after two to three successive passages into SI mice (Kuntz et al., 1991. Immunology 73, 356). In the present study, mixed HC transfer experiments showed that bg or wild HC could not prevent or delay neither the serological symptoms nor the pathology conferred by cotransferred mev HC. Nevertheless, when cotransferred with adoptive mev chimera HC, bg or wild HC could block the development of the pathology and the morbidity, although only delayed the emergence of the serological abnormalities. This shows that the differentiation of mev HC in a bg or wild normal-type environment does not allow the maintenance of all mev HC-dependent abnormalities.