Bovine serum TeBG was purified by 17 alpha -carboxyethynyl-17-hydroxy-4-androsten-3-one sepharose 4B affinity chromatography (T-sepharose) and hydroxylapatite column chromatography. The chemical and immunological properties of the purified TeBG were surveyed and the following results were obtained. 1) The procedures yielded 400 microgram of protein from 1 L of bovine serum with an overall purification of about 7,560 fold. 2) The purified TeBG was homogenous and was about 80,000 in molecular weight based on sucrose density gradient ultracentrifugation and polyacrylamide gel electrophoresis. 3) The antibody prepared against the purified bovine TeBG did not cross-react with dog and human sera, suggesting the species specificity of TeBG. 4) 125I-bovine TeBG, labelled by the lactoperoxidase method, had a high binding capacity to the anti-bovine TeGB antibody. These results indicate the applicability of purified TeBG and the antiserum for TeBG RIA.