Extracellular matrix (ECM) constituents likely play an important role in cell proliferation and the invasion of malignant human gliomas. We examined the formation of stress fibers and the growth of the human glioblastoma cell lines A172 and T98G cultured on collagen types I, IV, and V, laminin (LN), and fibronectin (FN). A172 cells cultured on LN and FN formed complete F-actin filaments after 24 h of culture and grew logarithmically after 48 h. In contrast, T98G cells on LN and FN reorganized only short F-actin filaments after 24 h of culture and grew rapidly after 72 h. However, on the collagen preparations, neither cell line formed definite stress fibers and both showed lower rates of cellular proliferation. Significantly positive correlation was observed between the relative intensity of F-actin filaments and the cell proliferation. The results indicate that the ability of ECM components to modulate the growth and differentiation of malignant glioma cells may be mediated, in part, by the assembly and disassembly of F-actin filaments.