Expression of transforming growth factor alpha (TGF alpha) is frequently associated with the development of human and animal tumors. Using a sensitive immunohistochemical assay, which can be applied on formalin-fixed, paraffin-embedded tissue, we have examined the expression of TGF alpha in 71 human gliomas (63 untreated and 8 recurrent tumors). Tumors were graded by a 3-grade-system: grade I = low grade gliomas, grade II = anaplastic gliomas and grade III = glioblastomas. A strong positive correlation between tumor grade and extent of TGF alpha expression was found (P less than 0.0001). Polymerase chain reaction (PCR) was used to amplify the fourth exon of the TGF alpha gene of 8 glioma DNA specimens and increasing amounts of normal human DNA, which served as a standard. No amplification of the TGF alpha gene copy number in tumors could be detected.