A protocol, based on the use of Pseudomonas lipase, is presented to measure quantitatively the amount of triacylglycerols in extracts from cultured cells of tissues. Since the lipase also acts on di- and monoacylglycerols, separation of the extracts by thin-layer chromatography is recommended. In order to allow the lipase-catalyzed hydrolysis to proceed efficiently, lipid extracts or eluates from silica scrapings were mixed with the detergent Thesit [dodecylpoly(ethylene glycol ether)], prior to drying. After dissolution of the dried residues in water, the amount of triacylglycerols was quantified using Pseudomonas sp. lipase, glycerol kinase, glycerol-phosphate oxidase, and peroxidase. The activity of the latter enzyme was followed either colorimetrically in the presence of 4-aminoantipyrine and 2,4,6-tribromo-3-hydroxybenzoic acid or fluorimetrically in the presence of homovanillic acid.