Diacylglycerol (DAG) is an important source of arachidonic acid, a signalling molecule and the precursor of the prostaglandins. In human platelet almost all the DAG produced from phosphatidylinositol degradation contains arachidonate (Takamura et al. 1987). DAG is hydrolysed by DAG lipase to 2-arachidonylglycerol (2-AG) which is further hydrolysed by monoacylglycerol lipase. 2-AG is an agonist of cannabinoid receptor 1.