This chapter presents the immunological parameters of the Aleutian disease of mink. The disease is of special interest because it serves as an excellent model of immune complex disease in which the antigen involved in the immune complexes is known. Viral infection produces a uniquely great antibody response with marked accumulations of plasma cells in the lymph nodes, spleen, kidney, and liver along with marked hyperglobulinemia. Immune complexes are readily demonstrable even by analytical ultracentrifugation, and viral antigen has been demonstrated in the complexes. Severe kidney disease develops in some animals, and viral antibody and antigen have been eluted from the kidney. The glomerular lesions are typical of an immune complex-mediated injury with fine granular deposits along the glomerular basement membrane that can be stained for Ig, C3, and viral antigen. Aleutian disease virus circulates as infectious antigen-antibody complexes in persistently infected mink. Smaller complexes are deposited in the glomeruli and arteries and cause severe and frequently fatal inflammatory lesions. Both the host genotype and the viral genotype influence the severity of Aleutian disease.