To determine the relationship between the structure and function of proteins coded for by the Ly-6 gene complex, we have transfected a cDNA for a Ly-6.2 specificity into COS-7 cells. A number of monoclonal antibodies which have been shown to be capable of inducing T cell activation and which have been previously considered to recognize distinct proteins all reacted with the same transfected gene product. The approach used in these studies should be useful to further elucidate the complexities of the Ly-6 alloantigen system.