A method for the detection and/or measurement in vitro of a lipase or phospholipase activity, including the addition of a sample likely to contain said lipase or phospholipase into the wells of microtitration plates coated with a layer of a lipid substrate which is able to be hydrolyzed by the lipase or phospholipase by releasing α-eleostearic acid, and the detection and/or the measurement of the lipase or phospholipase activity by UV spectrophotometry of the α-eleostearic acid released during the previous stage. The application of this method to the in vitro diagnosis of pathologies linked to an increase in the plasma lipase level.