Administration of an inactivated Aleutian disease virus vaccine to mink induced detectable antibody in one of 26 animals. When immunized mink were challenged with live virus, they developed more severe lesions than mink given a control vaccine. The immunized mink were also more susceptible to oral virus challenge than control mink. Passive administration of antiviral antibody at the peak of virus replication produced necrotizing acute inflammatory lesions, followed by mononuclear cell infiltrates.