Matrigel, an extracellular matrix material, has been used to promote growth of experimental tumors. SF-767, a human glioblastoma cell line, is used in brain tumor research. We investigated Matrigel induced changes in tumor latency, growth rate, cell yield, plating efficiency, and histology of SF-767 tumors in athymic mice. Low volume (0.1 ml) Matrigel did not increase growth rate in comparison with control tumors but appeared to promote uniformity in growth. High volume (0.5 ml) Matrigel increased the initial rate of tumor growth, increased cell yield and produced tumors with a centralized area of residual Matrigel and necrotic cells, with viable cells on the periphery of the mass. On average, tumors grown with Matrigel had shorter latency periods and lower plating efficiencies. We conclude that important characteristics of the SF-767 tumor model, which may be important when evaluating efficacy of anticancer agents, are altered by Matrigel.