We have analysed the role of the morphogenetic factors hepatocyte growth factor/scatter factor (HGF), neuregulin and E-cadherin in the process of metastasis and morphogenesis of mammary carcinoma cells. The cDNAs for HGF, neuregulin and E-cadherin were stably expressed in anaplastic human MDA MB 435 carcinoma cells. The altered cells were then injected into the mammary fat pads of nude mice, where they form tumors which can spontaneously metastasize to the lungs. We found that expression of HGF or neuregulin promoted metastasis whereas expression of the cell adhesion molecule E-cadherin was inhibitory. Moreover, expression of E-cadherin reconstituted the ability of the cells to form morphogenetic structures in matrigel cultures in response to HGF. These data demonstrate that HGF and neuregulin, which control branching or lobulo-alveolar morphogenesis of normal breast epithelium, do have metastasis-promoting effects on breast carcinoma cells. Moreover, our results suggest that the differential activities of the two factors can be explained by the degree of epithelial differentiation: induction of morphogenesis requires an intact epithelial adhesion and differentiation system, whereas induction of metastasis is observed when the cells have lost their epithelial characteristics.