To acquire some biological markers associated with the occurrence of acute graft-versus-host disease (aGVHD) after allogeneic bone marrow transplant (BMT) in children, we have studied the lymphocyte subset reconstitution and the percentage of peripheral blood mononuclear cells bearing HLA-DR and HLA-DQ class II molecules, This study included 37 allogeneic BMT: either with (n = 17) or without (n = 20) aGVHD. Within 2 months after transplantation, we observed that patients with aGVHD had a unique mononuclear cell profile characterized by (i) a significant increase in the percentages of CD8(bright+)CD28(-) T cells (P = 0.05) and CD3(+) T cells (P = 0.001), (ii) an important decrease in the percentage of CD56(+) cells (P = 0.0001), and (iii) a decrease in the percentages of HLA-DQ(+) and HLA-DR(+) monocytes (P = 0.001), and HLA-DQ(+) T lymphocytes (P = 0.0001), in comparison with patients without aGVHD. Moreover, statistical studies indicate that there was a positive correlation between CD8(bright)CCD28(-) and CD3(+) T cells, whereas CD3(+) T cells were negatively correlated to CD56(+) cells. We did not find any statistical correlation between the percentages of HLA-DQ(+) or HLA-DR(+) cells and the percentages of these lymphocyte subsets, Therefore, in this study done in children, we suggest that patients with (i) less than 20% of DQ(+) monocytes, (ii) less than 25% of CD56(+) lymphocytes, and (iii) an enhanced percentage of CD8(bright)CCD28(-) T cells are strongly associated with aGVHD. Unfortunately, these biological markers of aCVHD may not precede the clinical manifestations of the disease. (C) 1995 Academic Press, Inc.