Immunological cross-reactivity between feline and canine serum amyloid A protein (SAA) was studied to establish enzyme-linked immunosorbent assay (ELISA) with heterologous antibody. Purified feline SAA formed a precipitin line in immunogel double diffusion with anti-canine SAA antibody. Immunological cross-reactivity was similarly observed in ELISA. In sandwich ELISA with anti-canine SAA antibody, a dose-response curve was obtained over the range of 2 micrograms/ml to 123 micrograms/ml of purified feline SAA. From the present findings, the sandwich ELISA is found to have high repeatability for quantitation of purified feline SAA and may be applicable to determine the serum concentration of feline SAA.