Enzymic digestive method has been proved by us to be useful for the detection of some phospholipids, because many phospholipids are hydrophilic and boiled snake venom is a well-recognized pure source of phospholipase A2. Unfortunately, the enzyme is apt to be less active towards the phospholipids in formalin-fixed tissues than in fresh ones. From the present point of view, in regard to the structure and function of biological membranes“Fluid Mosaic Model”by Singer and Nicolson seems to be available. The biological membrane is composed of proteins and lipds. In comparison of the protein, there have been few researches towards a morphology of the membrane lipids.<BR>In the present paper, the digestive method with snake venom phospholipase was applied to guinea pig erythrocyte for the morphological observation of membrane's phospholipids. Some phospholipids in the cell membrane of intact red cells suspended in an isotonic buffer might be digested easily by snake venom phospholipase, because they are unfixed and are sufficiently in contact with the enzyme. Phospholipase can only act on the outer layer of intact red cell membrane on guinea pig red cells. The outer layer of membranes is mainly composed of lecithin. In this case, the lecithin is converted into lyso-derivative and fatty acid. Moreover, phospholipase is found to digest phospholipids in the washed intact red cell membrane without causing significant hemolysis, if the isotonic reaction medium contains no albumin. Therefore, the derived fatty acids should be converted to be insoluble soaps in situ, which could be used for the detection of digested phospholipids. By the way, the duplicate control sample was coducted in exactly the same medium except that phospholipase A had been omitted.<BR>Fresh samples of guinea pig blood were obtained by heart punction. In order to check the enzymic digestion, light-microscopic observation was carried out. This histochemical procedure is similar to Holczinger's method for the detection of fatty acids. The digested erythrocytes were colored dark green, but duplicate control materials were colored just gray. The percentages of Holczinger-positive red cells on the light-microscopic observations were counted after several durations of the digestion with several concentrations of Naja Naja phospholipase. More than 50 minutes of digestive process can introduce about 80% in the ratio of digested erythrocytes. Enzymic digestion was repressed by Glutaraldehyde fixation. As another check for the enzymic digestion, the derived fatty acids in the supernatant of the reaction medium containig albumin was determined biochemically. In comparison of the reaction medium containing neither albumin nor enzyme, free fatty acids increased definitely in the supernatant of reaction medium containing albumin. Therefore, the enzymic digestion was carried out on the cell membrane following this procedures, and the increased fatty acid might be derived from some phospholipids in the cell membrane.