EGF receptors were assayed by immunohistochemistry using a monoclonal antibody against EGF-R in 32 surgical samples of meningioma. EGF-R were found in all samples (32/32). Only tumor cells were stained and staining was homogenous in tumor tissue. EGF-R was simultaneously assayed by 125I-EGF binding on membrane preparation and immunohistochemistry on frozen sections in 10 meningiomas. Results were qualitatively equivalent in 9 cases. Staining intensity was not correlated with the histological type, the proliferative status of the tumor or the age and hormonal status of the patients. The immunohistochemical data are in agreement with previous biochemical assays on tissue homogenates.