We examined the potent inhibitory effects of interferon-alpha (IFN-alpha) on both cellular adhesion and cell proliferation of MCF-7 breast carcinoma cells. When MCF-7 cells were exposed to IFN-alpha at a concentration of 5x10(3) IU/ml for 5 days, cell proliferation was markedly inhibited. Cell attachment assay demonstrated that incubation with IFN-alpha for up to 48 h reduced alpha2beta1 integrin-mediated cellular adhesion. However, fluorescence activated cell sorter (FACS) analysis revealed that incubation with IFN-alpha for 24 h had no effect upon the cell surface expressions of either alpha2 and beta1 integrin on MCF-7 cells. These antiproliferative and antiadhesive actions of IFN-alpha may be applied to treatment for patients with metastatic breast carcinoma.