The medium conditioned by cultured rabbit aortic smooth muscle cells (SMC—CM) was used as the source of chemotacic factor. Its chemotactic activity for smooth muscle cells (SMCs) and NIH 3T3 fibroblasts were examined by mieroporous filter assay. The results showedthat the SMC—CM was chemotactic for SMCs but not for NIH3T3 fibroblasts,and the effects of SMC—CM on SMC migration were considered to be chemotacic rather than chemokinetic in nature.