Objective To investigate the antitumor effect of 17aα-D-homo-ethynylestradiol-3-acetae on the mice transplanted with melanoma (B16) tumor cells,and to explore the possible synergistic effect with irradiation.Methods IRM-2 mice transplanted with B16 cells were randomly classified into control group,irradiation group,17aα-D-homo-ethynylestradiol-3-acetae drug ( high dose,medium dose,low dose) groups,and drug and irradiation combination group.Mice in drug group and the combination group were intraperitoneally injected with 5,7.5,and 10 mg/kg drug for 7 days.Mice in the irradiation and combination group received 1 Gy total body irradiation at 4 d after drug injection and then once a day for 5 days.The tumor inhibition efficiency,the number of bone marrow cells,thymus indices,and spleen indices were evaluated.Results Tumor weights in each drug group were significantly lower than those of the control( t =4.58,9.07,6.67,P ＜ 0.05 ).Drug combinated with 137Csγ-rays enhanced the antitumor effect so that the tumor weights in the combination group were significantly decreased ( t =8.06,10.35,6.71,P ＜0.05 ) in comparison with the control groups.Moreover,the numbers of marrow nucleated cells,thymus index and spleen index in the drug group were higher than those in the control group ( t =2.64,3.80,2.84,P ＜ 0.05 ).Conclusions 17aα-D-homo-ethynylestrudiol-3-acetae can inhibit cell growth of B16 melanoma in mice and may also have radioprotective effect on the hematopoietic system and immune system of mice.