We have investigated cytokine gene expression in the two-way mixed lymphocyte cultures (MLC) enhanced by concanavalin A to assess whether this is a useful predictive method for severe graft-versus-host disease (GVHD) and graft failure in nine allogeneic bone marrow transplantation (allo-BMT) patients. Our present study revealed that increased IL-2, IL-5 and IFN-gamma mRNA expression and IL-2 and IFN-gamma production in the MLC in two cases with severe lethal transplantation-related complications (graft failure and grade III acute GVHD). These findings suggest that increased cytokine mRNA expression and cytokine products in this assay may be predictive of the development of transplantation-related complications.