It has been demonstrated that the epidermal growth factor receptor (EGFR) gene, the normal human counterpart of the viral erb-B oncogene, is amplified and overexpressed in over 50% of human malignant gliomas (HMGs). In the present study, analysis of the immunohistological staining characteristics of 57 HMGs using an anti-EGFR monoclonal antibody (mab) showed positive staining in 65% of the tumours with large cellular and regional differences in staining pattern and intensity. Screening a smaller number of HMGs with molecular hybridization techniques revealed 10/21 glioblastomas (48%) amplified for the gene; of 11 glioblastomas studied by Northern blot hybridization, 7 tumours with gene amplification showed RNA overexpression, the remaining 4 without amplification did not. Regional differences in DNA levels were observed by Southern blot in 2 tumours; in one particular case, amplification and overexpression were found to be localized to one half of a single HMG, the other half showing neither EFGR gene amplification nor overexpression.