CD45RC^low CD8 T cells prevent graft-versus-host disease (GvHD) induced by allogeneic CD4 T cells. Purified CD4 T cells from LEW rats (6 × 10⁶ cells/rat) were transferred into (LEW × BN) F1 rats 24 hours after total body irradiation (4.5 grays) either alone (group 1, ▴; n = 10), or in combination with 3 × 10⁶ LEW CD45RC^high CD8 T cells (group 2, ▪, n = 10), CD45RC^low CD8 T cells (group 3, ○, n = 11), or unfractionated CD8 T cells (group 4, ⊠, n = 7). Control rats were irradiated and injected with PBS (□, n = 4). Recipients were examined for induction of acute GvHD as revealed by weight loss and mortality. The comparison of maximal weight loss by ANOVA revealed statistical differences between the following groups: group 1/group 3: P < .01; group 1/group 4: P < .05; group 2/group 3: P < .01; group 2/group 4: P < .05; and group 3/group 4: P < .01. The statistical analysis of survival using χ₂ test showed statistical differences between the following groups: group 1/group 3: P < .01; group 2/group 3: P < .01; and group 3/group 4: P < .01.