Mice suffering from melanoma can be cured by treatment with a recombinant antibody-lymphotoxin-alpha fusion protein. In order to characterize the involvement of T cells in this syngeneic tumor model, the T cell receptor repertoire was analyzed both quantitatively and qualitatively. In this connection, quantitative analysis of the T cell receptors displayed only a modest overexpression in some of the variable beta chain families over the course of therapy. Clonotypic mapping, however, revealed a marked increase in the number of clonally expanded T cells among the tumor-infiltrating T cells, suggesting a specific activation.