Feline infectious peritonitis (FIP) is a fatal disease of domestic and exotic cats. Current feline coronavirus antibody titer tests are useless for diagnosing FIP in the live cat. A sensitive and specific test for diagnosis and screening is needed. We are currently investigating the usefulness of an antibody assay that uses a purified viral protein. This protein may be expressed by the virus only in infections that lead to the production of disease. Therefore, use of this protein in a diagnostic assay could distinguish the disease-causing virus from the nonvirulent virus. We propose to produce this protein for development of an enzyme-linked immunosorbent assay (ELISA) to detect antibodies specific for this viral protein. We will then screen cats with FIP and healthy cats seropositive for FCoV to determine if antibody to this protein occurs only in cats with FIP.