Graft-versus-host disease (GVHD) is caused by donor T lymphocytes that recognize foreign antigens on host tissues. This leads to T cell activation, which involves a cascade of events including the transcription of genes for cytokines and their receptors and the production of cytokines. One of the first cytokines to appear is interleukin 2 (IL-2). IL-2 production enhances the IL-2 receptor expression and leads to T cell proliferation. As a further step, differentation of T cells occurs, which results in the production of a certain pattern of cytokines. These cytokines influence the expression of cell surface antigens and adhesion molecules, and are able to activate other cell types such as cytotoxic T cells, macrophages and natural killer cells, which might act as effector cells in tissue destruction. Insight into the sequential expression of the various cytokines involved might enable a more effective treatment of GVHD. Therefore, we investigated the occurrence of cytokines in a murine model for acute GVHD. We addressed in particular the period early after allogeneic reconstitution.