Aleutian disease is an immunological disease of mink caused by a persistent virus infection. Recently Aleutian disease viral antigen has been extracted from tissue of mink early in the course of infection and the Aleutian disease virus has been isolated. The virus particles were similar in morphology and size to certain parvovirus having a 23 nm diameter, spherical shape and icosahedral capsid. Recent developments in serological techniques, i.e. immunofluorescence, complement fixation, countercurrent electrophoresis and immunodiffusion, have enabled rapid progress toward understanding the nature of the disease. It is suggested that the hypergammaglobulinemia is due to overproduction of IgG antibody specific for the Aleutian disease virus. The glomerulonephritis, vasculitis, positive antiglobulin test, systemic proliferation of lymphocytes and generalized plasmacytosis in Aleutian disease are believed to be the results of a continuing host antiviral immune response, the persistence of the virus in the presence of high level of specific antibody and the formation and deposition of the immune complexes.