Phosphatidylinositol 4,5-bisphosphate specific phospholipase C has been detected in a membrane preparation fromPharbitis nil cotyledons. The enzyme has a pH optimum of 6.8 and activated by calcium ions, deoxycholate, phosphatidylinositol and phosphatidylethanolamine. The enzyme is inhibited to varying degrees by Tween 20, Triton XI00, zinc, copper, cobalt and manganese ions and phosphatidylserine. G-protein activators do not affect the activity ofPharbitis nil phospholipase C. Analysis of the products of the reaction by HPLC shows inositol 1,4,5-trisphosphate from phospholipase C and inositol bisphosphate from inositol-1 and -5 phosphatase activity.