Phosphatidylinositol-specific phospholipase C (PLC) enzymes catalyze the hydrolysis of phophatidylinositol 4,5-bisphosphate [PtdIns(4,5)P 2 ] to diacylglycerol (DAG) and inositol 1,4,5-triphosphate [Ins(1,4,5)P 3 ]. PLCε is a recently discovered isoform that has been shown to be activated by members of the Ras and Rho families of guanosine trisphosphatases (GTPases) as well as subunits of heterotrimeric G-proteins. We describe a method for expressing a truncated PLCε variant as an MBP fusion protein in E. coli. Subsequently, we describe the methodology necessary to reconstitute this protein with K-Ras-4B and RhoA GTPases and measure its activation.