We performed in situ hybridization (ISH), using radioactively labeled deoxyoligonucleotides, to localize endothelin (ET) receptor subtype mRNAs (ETA and ETB) in a series of meningiomas in comparison to normal human meninges. Our examination also addressed the cerebellum adjacent to the meninges investigated. Tumor cells of all meningiomas examined showed strong hybridization signals for ETA receptor mRNA, whereas for ETB receptor mRNA only weak hybridization signals could be detected in endothelial cells of tumor blood vessels and in some cell clusters. mRNAs for neither ET receptor were detectable in normal leptomeninges. In human cerebellum we found ETA receptor mRNA only in large blood vessels; ETB receptor mRNA was intensely expressed in Bergmann glial cells. Neither subtype was detectable in neurons.