Publisher Summary This chapter describes the bioluminescent assay for lipase, phospholipase A 2 , and phospholipase C. The dim mutant M17 of the marine luminous bacterium Beneckea harveyi MAV #392 emits light with either exogenous aldehydes or fatty acids. The triple aldehyde mutant, M 17 LP lacks protease, lipase, phospholipase A, and phospholipase C activities, yet it retains the response to fatty acids and aldehydes. Phospholipase A 2 activity is assayed either continuously or discontinuously as described for lipase except that an ethanolic solution of the desired concentration of phosphatidylcholine, preferably L -α-dimyristoylphosphatidylcholine, is injected instead of trimyristoylglycerol. Phospholipase C activity is assayed in a coupled enzyme assay with phosphatidylcholine as substrate and lipase as an auxiliary enzyme. The phosphatidyl-choline is hydrolyzed to diacylglycerol, which is then hydrolyzed further by the lipase to yield free fatty acids. It is found that conditions for the coupled enzyme assay are selected, such that excess of pancreatic lipase is present to hydrolyze the diglyceride as it is being formed.