In a panel of wild mice trapped in different geographical regions, the concomitant expression of V beta 17 T cell receptors and I-E histocompatibility molecules is frequent. By Southern blot analysis, eight forms of V beta 17 genes have been distinguished that encode five kinds of V beta 17 domains. Populations of Asia display the highest level of polymorphism and include all the V beta 17 forms and domains. The V beta 17 T cells of wild origin are deleted in mice expressing Mls-3 and related superantigens. Wild mice use V beta 17 domains different than the one of laboratory strains. Together with endogenous superantigens polymorphism, this accounts for the observed low frequency of clonal deletion cases in natural populations.