Chronic graft-versus-host disease (GVHD) accompanying autoimmune disease was induced in (C57BL/6xDBA/2) F(1) mice (H-2(b/d)) by an injection of splenic T cells of parental DBA/2 origin (H-2(d)). In parallel with the onset of proteinuria, an expansion of lymphocytes was induced in the liver and kidney, showing a peak at 2 weeks after the onset of disease. The majority of lymphocytes were of recipient origin (H-2(b/d)). The main lymphocyte subset among T cells at the pre-onset stage and after the onset of disease was CD8(+) NK1.1(-) CD3(int) cells (of extrathymic, hepatic origin) in both the liver and kidney. NK1.1(-) CD3(int) cells confer primarily neither NK-like nor NKT-like cytotoxicity. No induction of these types of cytotoxicity was observed in these mice with the expansion of NK1.1(-) CD3(int) cells. This raised the possibility that granulocytes induced in the liver and kidney might be associated with tissue damage. The present results suggest that, similarly to the case of autoimmune-prone mice with genetic background (e.g. MRL-lpr/lpr mice and BXSB mice), NK1.1(-) CD3(int) cells of extrathymic, hepatic origin might be crucial lymphocytes involved in the induction of the autoimmune-like disease in mice with chronic GVHD, in conjunction with Bcells (e.g. B-1 cells).