Immunosuppressive soluble factors such as transforming growth factor beta and cell surface molecules such as FasL may contribute to the immune evasion of malignant glioma. B7 homolog 1 is a member of the B7 family of costimulatory molecules implicated in the negative regulation of T cell immune responses. Here, we show that human glioma cell lines express B7 homolog 1 protein that reduces interferon-gamma production by activated T cells. The expression of B7 homolog 1 in vivo was demonstrated in a large series of human glioma samples, with a significant correlation between the level of B7 homolog 1 expression and the tumor grade. Overall, our data suggest that B7 homolog 1 may be involved in the immune evasion of glioma and encourage the blockade of this pathway in future immunotherapies.