Feline infectious peritonitis (FIP) is perhaps the most devastating infectious disease of cats, and there remains a desperate need for a fast and reliable diagnostic test. FIP is caused by the Feline Infectious Peritonitis Virus (FIPV), which has undergone a subtle mutation from its normal gastrointestinal counterpart, Feline Enteric Coronavirus (FECV). Clinical signs in the cat are vague and nonspecific, and can include inappetence, lethargy, disorientation, vomiting and diarrhea. These vague symptoms mask the underlying severity of an otherwise rapidly fatal condition. Unfortunately, a definitive diagnosis of FIP is often challenging and is typically a diagnosis of exclusion in living patients, which is frustrating for owners and veterinarians, alike. While several assays capable of confirming FIP have been developed, these tests can require invasive methods and lengthy wait times for results. In contrast, if the virus itself does not provide a definitive fingerprint, researchers may need to rely on the host response to provide a diagnosis. Powerful new approaches to characterize the molecules present in patient blood can now be employed in the cat to interrogate hundreds of plasma proteins and potentially identify a characteristic set of FIPV biomarkers that reflect the presence of mutated virus. These biomarkers can then be applied to a rapid and affordable prognostic and/or diagnostic test that can be offered by primary care clinicians at wellness exams and/or when FIP is clinically suspected. If successful, this assay could allow rapid and definitive diagnosis of FIP, providing much-needed peace of mind in an otherwise heartbreaking situation.