Functional studies concerning the unique interaction between class I H-2 allodeterminants and cytolytic T lymphocyte (CTL) antigen receptors have benefitted from the development of H-2Kb mutant mouse strains and somatic H-2 variants selected with monoclonal antibody. Here, we describe the development of a novel approach to immunoselection of somatic H-2Kb variants employing a Kb-specific CTL clone as the negative selective agent. The rationale for this method is that the use of an alloreactive CTL clone as the selective agent should enable us to detect the emergence of structural Kb variants based on their loss of the relevant CTL-defined allodeterminant. Thus, these structural variants are well suited to an in-depth analysis of the functional relationship between H-2 antigens and receptor recognition by CTL. Using this approach, we successfully isolated two types of structural Kb variants, as well as numerous Kb-loss variants. The functional studies described in this paper indicate that these structural variants exhibit alterations in expression of both CTL-defined and serologically defined H-2Kb allodeterminants. The structural characterization of such variants should enable us to identify the precise amino acid residues responsible for the creation of the relevant CTL-defined Kb allodeterminants.