Diacylglycerol (DG), a product of the hydrolysis of some phospholipids, isthought to play important functions as a second messenger. DG can activate intracellular protein kinase C (PKC), which in turn phophorylates a variety of proteins and generates cellular effects. On the other hand,as an important intermediate of lipid metabolisms, DG in vivo is also involved in regulating lipid metabolisms and hormone cycles. The present researches on the mechanisms of the modulation of cellular functions by DG, are mostly concentrating on its effects on cellular signalling transduction.