The effect of gammaglobulin treatment on autoantibody production was investigated in SCID mice reconstituted with human peripheral blood mononuclear cells (PBMC) obtained from patients with PBC. All reconstituted mice displayed the presence of human antimitochondrial antibodies (alpha M2Ab) of both IgG and IgM types before treatment with human immunoglobulin. Two weeks after i.p. injection of 20 x 10(6) PBMC into SCID mice, i.p. treatment with various preparations of human immunoglobulin was initiated. In control animals treated with saline, serum levels of human alpha M2Ab of the IgG type increased with time, peaking around 4 weeks after reconstitution. In contrast, human IgG autoantibodies rapidly decreased in all animals treated with human IgG. Treatment with a human IgM preparation had no effect on serum levels of alpha M2Ab of the IgG type. The results may suggest that the pronounced reduction of specific IgG autoantibodies was due to an increased catabolism of human IgG, including the autoantibodies, in the gammaglobulin-treated mice. Although the production of human alpha M2Ab in reconstituted mice could be easily shown, PBC-specific liver lesions or bile duct destruction were not observed, irrespective of treatment protocol.