1. By cellulose column chromatography, phosphatidyl-serine was isolated from three fractions, obtained from pig erythrocyte lipids by silicic acid column chromatography. The total yield was 81% on the basis of the value determined by Dawson\u27s method. 2. One of the preparations (yield : 27%) was confirmed to be in high purity, by elemental analyses, by infrared spectroscopy and by various paper- and thin layer-chromatography. 3. The occurrence of phosphatidyl-serine in two different ionic forms ; mono-basic and di-basic ones, is shown by cation analyses as well as by infrared spectra. The cations in the native preparations are composed mainly of bivalent ions such as Ca++ and Mg++. 4. The gas chromatographic data showed that the fatty acids of phosphatidyl-serine were composed mainly of C-18 acids (91.7%) ; stearic (31.4%), oleic (54.5%), and linoleic acid (5.2%)and of C-16 acid ; palmitic acid (5.3%)
