Interleukin-7 (IL-7) is known as a growth factor for pre B-cell and mature T-cells in human. But in leukemic cells, IL-7 effect is variously reported. To investigate the effect of IL-7 on the cells of childhood acute leukemia we used 3H-Thymidine assay. Twelve Acute lymphoblastic leukemia (ALL), seven T-ALL and three Acute myelogenous leukemia (AML) were involved in this study. Two out of twelve ALL and three out of seven T-ALL bone marrow (BM) cells were stimulated by IL-7 in 3H-Thymidine incorporation. In normal and AML BM cells, IL-7 had no stimulatory activity as in various leukemic cell lines. Two normal peripheral blood T-cells responded to IL-7 dose dependently. We have seen the effect of IL-7 to stimulate T-lineage cells but, for precise conclusion, further study using more purified samples will be needed.