✓ Surgical specimens from six benign and 16 malignant human gliomas were investigated immunohistochemically to correlate the degree of malignancy, the distribution of transforming growth factor-alpha (TGF-α) and epidermal growth factor (EGF) receptor, and the potential for cell proliferation using monoclonal antibodies to TGF-α, EGF receptor, and Ki-67. Fourteen (88%) of the malignant gliomas and one (17%) of the benign gliomas were found to be positive for TGF-α, and 14 (88%) of the malignant gliomas and two (33%) of the benign gliomas expressed EGF receptor. The proliferation index with Ki-67 was 18.8% ± 8.1% (mean ± standard deviation) in malignant gliomas and 1.9% ± 1.8% in benign gliomas. In general, cells positive for EGF receptor and Ki-67 were randomly distributed throughout the tumor tissue, and cells positive for TGF-α tended to be clustered without obvious relationship to areas of necrosis or blood vessels. In some tumors, cells positive for TGF-α, EGF receptor, and Ki-67 were associated in a focal distribution. The more frequent expression of TGF-α and EGF receptor in the highly proliferative malignant gliomas is compatible with a role for TGF-α and EGF receptor in the induction or stimulation of malignant gliomas.