Brain angiogenesis inhibitors (BAI) are putative transmembrane proteins containing an extracellular domain with thrombospondin type-1 repeats which can exhibit anti-angiogenic activity. BAI1 mRNA is expressed mainly in the brain, while BAI2 and BAI3 mRNAs are more widely expressed. We hypothesized that the BAI family might have anti-tumoral properties and studied the expression of BAI1 protein in normal human brain and in glioblastoma multiforme. We generated an anti-BAI1 antibody and showed that BAI1 was widely expressed in normal brain but was absent in 28 glioma cell lines and in the majority of human glioblastoma investigated. BAI1 expression did not correlate with TP53 status and we did not confirm previous findings that p53 regulates BAI1 mRNA expression in glioma cells. The finding that expression of BAI proteins may be lost during tumor formation is of special interest as restoration of their function in tumors may be of therapeutic benefit.