Radioligand binding assay and competitive radio-assay of ¹²⁵I-EGF on plasma membrance EGF receptor and radio-receptor assay when ¹²⁵I-EGF was incubated with human glioblastoma multiforme cells were carried out. The results showed that there is a high affinity binding site on BT325 cells plasma membrance, exogenous GM3 could not alter the affinity (K_d) of EGF binding with cell-surface receptors, but decrease the receptor number. GM3 could significantly prolong the endocytosis process of EGF-EGFR complex. The concentration of EGF in culture medium was unchanged by GM3 and BBG,but that of EGF in cytoplasm was increased by GM3. It suggested that GM3 might inhibit the secretion of EGF.