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T lymphocytes play a pivotal role in graft-versus-host disease (GVHD) and largely contribute to the graft-versus-leukemia (GVL) effect. Most mature T lymphocytes specifically recognize antigens through the α/βT-cell receptor (TCR). Each α/β TCR chain includes a constant region and a variable region, the latter being encoded by V-Jα or V-D-Jβ rearranged gene segments. To better characterize T cells involved in GVHD, Vα and Vβ gene segment usage was analyzed, after cDNA amplification, in peripheral blood mononuclear cells (PBMC) and skin samples from three patients with grade II cutaneous GVHD. At time of GVHD diagnosis (days 11, 22, and 25), when first signs of engraftment were detectable, virtually all Vα and Vβ subfamilies were represented in PBMC RNAs of the three recipients. These results suggest that diversified TCR gene segment expression is observed early after allogeneic bone marrow transplantation (alloBMT). Lymphocytes infiltrating GVHD skin also expressed a large series of Vα and Vβ subfamily specificities. However, analysis of the Vα and Vβ amplified products showed substantial differences between PBMC and the skin lymphocyte RNAs. These observations indicate that a large variety of T lymphocytes are present at the disease site, while some of them may be specifically amplified or decreased in response to minor histocompatibility antigens (miHA). Further characterization of the latter T-cell subpopulations should lead to a better understanding of human in vivo responses directed at miHA.