Two partial antagonists of human interleukin-2(IL-2):15 Val-IL-2,126Asp-IL-2 and an IL-2 receptor a subunit binding deficient mutant 62Leu-IL-2 have been obtained by site-directed mutagenesis, 62Leu-IL-2 could exhibit significant stimulation on CTLL-2 cells. When 15Val-IL-2 or l26Asp-IL-2 was incubated together with CTLL-2 cells in addition to 62Leu-IL-2,the stimulative ability of 62Leu-IL-2 was distinctly inhibited.In consideration with the interaction of IL-2 with IL-2 receptor subunits,15Val-IL-2 or l26Asp-IL-2 can be used for the primary determination on receptor subunit binding ability of IL-2 mutants. Furthermore，this idea may also be applied in some other ligand-receptor systerns.