We have previously demonstrated that human brain tumor cells, in particular glioblastoma multiforme (GBM), express abundant receptors for interleukin-13 on the cell surface. These receptors are composed of IL-13 receptor (IL-13R)alpha1, IL-13Ralpha2, and IL-4Ralpha chains. The significance of overexpression of IL-13R on tumor cells is not known. Because expression of IL-13R on glioma cells is an unexpected phenomenon, we examined whether these receptors are polymorphic. Therefore, we analyzed cDNA for IL-13Ralpha1 and IL-13Ralpha2 chain genes by PCR-based single-strand conformation polymorphism and direct sequencing techniques for a possible polymorphism in 19 GBM, one normal human astrocyte, and two fibroblast cell lines. All analyzed samples except normal astrocytes overexpressed IL-13Ralpha2; however, none of these cell lines showed a mutation in cDNA for IL-13Ralpha2 chain. In contrast, all GBM samples, normal astrocytes, and fibroblasts expressed mRNA for IL-13Ralpha1 with apparent single nucleotide polymorphism in the transmembrane domain. To study the function of IL-13R on brain tumor cells, we investigated the regulation of adhesion molecules by IL-13 as assessed by flow cytometric analysis. A172 cell line expressed a low level of vascular cell adhesion molecule-1 (VCAM-1), while U251 and LA1-5g cell lines expressed intercellular adhesion molecule-1 (ICAM-1). On the other hand E-selectin was not expressed in any cell lines. Interestingly, IL-13 increased the expression level of VCAM-1 in A172 cell line in a dose- and time-dependent manner. However, IL-13 did not modulate any other adhesion molecules. These results suggest that IL-13R on GBM cells are not rearranged but appear to be functional.