Diarrhea is an extremely common and clinically significant problem in cats, and the intestinal parasites, Giardia and Cryptosporidium, play an important role in many of these animals. The detection of these parasites in fecal specimens can be difficult, because the organisms can be shed intermittently, and because their detection can be confused with many artifacts such as grass, pollen, and yeast. The need for accurate identification of these parasites in diarrheic cats often leads to injudicious antibiotic therapy, which can exacerbate the diarrhea. Many veterinarians and reference laboratories have resorted to using alternate tests such as ELISA tests that rely upon a reaction between an antibody in the kit and antigen in the organism to cause a color change that denotes a positive test. However, virtually all of these tests are marketed for use in humans, and their performance characteristics have not been validated in the cat to date. Our preliminary studies have shown that many of these tests have unacceptably low sensitivities. The aim of this study is to evaluate and compare the performance characteristics of 5 ELISA tests with fecal flotation and immunofluorescence in 200 diarrheic cats for the detection of Giardia and Cryptosporidium. These results will have a direct impact on assisting veterinarians and reference laboratories in proper selection of diagnostic tests to improve the diagnostic yield of these important parasites and facilitate their proper treatment.