Feline infectious peritonitis is a common fatal disease in cats from pedigreed catteries and shelters. The disease is almost impossible to manage or treat, partly because it is difficult to diagnose and there is little information about immunity to the infection. Also, cats vary amongst themselves with respect to the types of lesions they develop, the way their disease manifests, and their ability to cope with the infection. In neurological FIP, the pathology and immunology are much more homogeneous than forms of FIP affecting the entire cat, i.e. “wet” or “dry” FIP. Thus, neurological FIP appears to be a good system for establishing some baseline understanding of the way the virus and the immune system interact in this disease. The proposed research compares a panel of immunological chemical messages in the brain tissue of FIP-affected cats with brains of cats without neurological FIP, and characterizes major changes in their immune status. Subsequently, a pilot study is proposed, which intervenes in cats with neurological FIP by either replacing a deficient immune chemical or using antibodies against abnormally elevated immune chemicals. Based on this information, we hope to understand major problems with the immune system in FIP and have preliminary data on how to correct these abnormalities.