Systemic amyloidosis was induced consistently in mice by intramuscular injection of syngeneic organ (liver and kidney) extracts mixed with CFA six times at weekly intervals. Syngeneic organ extract with CFA also induced amyloidosis of a lesser degree. All three strains of mice (C57BL/6, C3H/He, and BALB/c) injected with a syngeneic liver extract mixed with CFA developed systemic amyloidosis; the most prominent amyloid deposition occurred in C57BL/6 (B6) mice, followed by C3H/He and BALB/c. The amyloid substance deposited in these animals was identified as mouse amyloid A protein (AA). Furthermore, an organ specificity of the immunogen in inducing amyloidosis was suggested with liver and kidney extracts. Primed spleen cells of the immunized B6 mice were fractionated by a nylon-wool column and injected to normal recipient mice via the tail vein. Organs of the recipient mice developed systemic amyloidosis 8 wk after the transfer, and the most prominent histological changes occurred in the recipient mice given nylon-wool column adherent spleen cells. Using anti-Thy-1,2; Ly-1; Ly-2, antibody and complement, it was suggested that T cells, especially Ly-1,2,3+ T cell populations in the primed nylon-wool adherent cells, play an important role in the induction of systemic amyloidosis. It was shown further that the amyloidosis-inducing substance in liver extract was composed of unstable proteins or protein-bound substance.