We have previously shown that conditioned medium (CM) from metastasizing human salivary gland adenocarcinoma cell clones contains factor(s) that stimulate the proliferation and migration of bovine aortic endothelial (BAE) cells, and inhibit the production of collagenases by BAE cells (Azuma M. et al. (1993) Cancer Lett., 73, 85-93). To further characterize this, we evaluated the expression level of epidermal growth factor (EGF) secreted by a non-metastasizing cell clone (HSGc) and its metastasizing cell clones, and analysed the effect of EGF on the biologic behaviors of BAE cells. When the secretion of EGF by cell clones was estimated by enzyme-linked immunosorbent assay, metastasizing cell clones released a large amount of EGF as compared with HSGc. However, the number of EGF receptor was detected consistently at a level that was similar in all cell clones. With regard to the effect of EGF on the malignant potential of cell clones such as proteolytic aggressiveness, EGF did not affect the secretion of both collagenases and their inhibitor from cell clones. Alternatively, exogenous EGF stimulated the proliferation and migration of BAE cells, and inhibited the secretion of collagenases from BAE cells. Neutralization with a neutralizing antibody of EGF released into CM abolished the inhibitory effect of CM on the secretion of collagenases from BAE cells. Thus, the CM-contained factor, which is responsible for the induction of biologic behaviors of BAE cells, can be attributed to EGF.