A digestive enzyme system exists in Daphnia that enables it to digest considerable protein and carbohydrate within 30 min. The amount of proteinase per body weight of Daphnia is approx. 200 times greater than that per body weight of hog. This proteinase of Daphnia simulates that of mammalian trypsin. It was demonstrated qualitatively, by micromethods, from the glycerol extract of D. magna intestines. Quantitative estimations were made of the proteinase activity of extracts of whole D. pulex. In all cases similar extracts of hog pancreas were compared with the Daphnia extracts. No pepsin was found in the Daphnia digestive system. Amylase and lipase were chemically demonstrated in the extracts of Daphnia. The pH of the gut of D. magna was 6.8-75.