Arachidonic acid has been implicated as a second messenger in numerous systems, and many agonists stimulate the intracellular accumulation of arachidonic acid ( 1 , 2 ). Arachidonic acid may be generated by phospholipase A 2 hydrolysis of phospholipids, or by hydrolysis of diacylglycerol through the sequential action of diacylglycerol lipase and monoacylglycerol lipase ( 3 – 6 ). These activities can be easily measured using sensitive radiometric assays as described herein. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.