The monocyte-depleted peripheral blood mononuclear cells were separated into CD4,+, and CD8,+, subpopulations by panning technique with McAb CD4 and CD8. The purity of CD4,+, and CD8,+, cells was 89.2% and 85.8% respectively, which was estimated by an indirect immunofluorescence technique. The radiosensitivities of CD4,+, and CD8,+, cells and the effect of DNA synthesis in both cells' subpopulations influenced by Vit A were assessed by ,3,H-TdR incorporation. The experimental result showed that after γ-radiation in different doses on CD4,+, and CD8,+, cells, the ,3,H-TdR incorporation was significantly decreased. The ,3,H-TdR incorporation rate in CD 8,+, cells irradiated with addition of 5 µg/ml Vit A increased significantly (,p,<,0.05).