Purified bovine growth hormone (bGH) and human growth hormone (hGH) have been covalently bound to Sepharose 4B gel utilizing cyanogen bromide as the activating agent. Under the conditions employed, up to 1.44 mg of bGH and 1.20 mg of hGH were covalently bound per ml of settled Sepharose. Although growth hormone linked to Sepharose retained immunological activity in the complement fixation assay, the curve was significantly shifted in the direction of higher antigen concentrations and a zone of antigen excess was not attained with bGH—Sepharose. The observation that mixtures of unconjugated bGH or hGH and Sepharose gave complement fixation curves similar to that for bGH or hGH alone confirms that the covalent binding of growth hormone directly to Sepharose is accompanied by structural changes in the hormone or steric effects which alter the reactivity of the antigenic sites. This, however, did not interfer with the use of the bGHand hGH—Sepharose conjugates for purification of specific antibody from antisera. Purified antibody, eluted from appropriate columns of immobilized hormone with guanidine hydrochloride, reacted normally with unconjugated growth hormone by immunodiffusion and in the complement fixation assay. (Endocrinology92: 431, 1973)