Four Blastomyces antigens ERC-2 (B. gilchristii, dog, Wisconsin), B5929 (human, Minnesota), 597 (human, Wisconsin), and T-27 (polar bear, Tennessee) were tested against 31 serum specimens from dogs with blastomycosis and 19 from healthy dogs. All antigens detected antibody; efficacy varied. ERC-2 showed the highest ELISA mean absorbance value of 3.00 followed by T-27. Test performance varied by sample geographic origin. Further study is needed to determine if ERC-2 antigens may be clinically useful, and whether the combination of the particular fungal species as antigen source, host animal, and the species and geographic location of the patient being tested is important for optimum test characteristics.