To understand the role of mesangial matrix in regulating responses of mesangial cells (MCs), particularly as a cause of disease, we examined the behavior of MCs cultured in a three-dimensional extracellular matrix (ECM). Mouse and rat MCs were incorporated into ECM composed of type I collagen gel matrix (CGM) and basement membrane-type gel matrix (BGM), and their shape and proliferation were assessed. The effect of gel matrix on MC migration was also studied. MCs exhibited marked elongation and proliferation in CGM, whereas these behavior were inhibited by increasing the ratio of BGM. Although CGM allowed MC migration, BGM restricted it to a great extent. To identify the cause of our findings, we examined the effects of ECM components in our experimental system. Laminin, fibronectin, type IV collagen, and heparin-like proteoglycans (heparan sulfate and heparin) were each mixed separately with CGM at a concentration of 50 micrograms/ml gel. Whereas fibronectin promoted MC elongation and proliferation, and laminin inhibited MC migration, type IV collagen and heparin-like proteoglycans inhibited all three activities of MCs. Our findings suggest that basement membrane-type mesangial matrix is important in regulating the behavior of MCs in vivo.