Although both amphiregulin and TGF-alpha are known to exert their effects through the EGF receptor, we find that concentrations of recombinant human amphiregulin and TGF-alpha that are equipotent in EGF receptor activation and mitogenesis exhibit markedly different effects on MDCK cell morphology. Amphiregulin induces a spindle-like morphology that is associated with a redistribution of E-cadherin from a Triton-insoluble to Triton-soluble pool. TGF-alpha does not affect epithelial morphology nor does it affect the distribution of the Triton-soluble or -insoluble pool of E-cadherin. The effects of amphiregulin on E-cadherin are associated with actin rearrangement. The morphological and biochemical effects of amphiregulin are prevented by EGF receptor blockade but require Src-family kinase activity and MAPK signaling. These results identify an action of amphiregulin that is distinct from TGF-alpha that may contribute to amphiregulin's participation in the pathogenesis of inflammatory disorders like psoriasis and cancer.