The immunochemical reactivities of theαA andαB subunits from bovineα-crystallin have been compared using 5 monoclonal antibodies and 2 polyvalent antisera. Each subunit bound the same maximum amount of antibody, regardless of its source, and each subunit was able to completely displaceα-crystallin from its antibodies. One monoclonal antibody (463–122) and mouse anti-αB polyclonal antiserum bound equally well to the two subunits; with the other monoclonal antibodies and an antiα-crystallin antiserum, the affinities for theαA chains were about 103fold higher than those for theαB chains.These observations indicate that theαA andαB subunits of bovineα-crystallin share several similar, but not necessarily identical, cross-reacting antigenic determinants. The reasons for the differences between these observations and those of other investigators are discussed.