Treatment of large burns would be simplified by the development of a nonsensitizing allograft which would survive permanently. In our hands, in vitro immune modification of the allograft has prolonged graft survival in mice across major histocompatibility barriers (H-2d to H-2b) by 36% (steroid pretreatment) and 25% (monoclonal antibody to the Iad antigen found on donor Langerhans cells). To our knowledge, monoclonal antibody has not been employed in this capacity previously. Double grafting studies suggest that neither MK-D6 nor steroids enhance graft survival by systemic immunosuppression. Moreover, MK-D6 acts upon the afferent limb of the immune response while steroids interrupt the efferent limb (and probably afferent limb). These effects are not additive. This modest improvement in allograft survival may have profound importance since allografts supported briefly by host immunosuppression have gone on to indefinite survival in burn victims without further immunologic intervention. This improvement in allograft survival is of fundamental immunologic interest. If synergistic pretreatments can be found, it may ultimately allow allografting of burn victims with the expectation of indefinite graft survival.