Amajor role in sustaining tumors like gliomas has been attributed to growth factors. Many questions remain unanswered about how such external signals are transduced into a transformed phenotype. Growth factors such as PDGF and epidermal growth factor(EGF) activate PLC, and this activation requires the intrinsic tyrosine kinase activity of the growth factor receptor. There are only a few reports on PKC activity in astrocytoma cells, especially in human glioma cells. We focused on signal transduction of phospholipase C(PLC) and phospholipase D(PLD) in human glioma cells. In this study, using genistein and calphostin C, the regulation of PLC, PLD, and PKC was investigated. The results are as follows; 1) Genistein is a selective inhibitor of PDGF-induced PLC- and PLD activation in T98G glioblastoma cells but not in Hs 683 glioma cells. 2) Calphostin-C stimulates PLC and PLD, possibly through a PKC-independent pathway in both T98G and Hs 683 cells. 3) Both genistein and calphostin-C inhibit glioma cell proliferation, indicating that the pathway for activation of PLC and PLD is not relevant to the pathway of cell proliferation in glioma cells.