Thirty g. of dried, powdered glycerophos-phatides from the ether extract of human brain are dissolved in 275 ml. hot benzene, 75 ml. of conc. Na alcoholate added, and the mixture heated for 1 hr. in a pressure flask in a boiling water bath. After standing all night at room temp., the mixture is centrifuged, the supernatant soln. concd. in vacuo, precipitated with acetone and 4-5 g. of a mixture of apparently N-containing and N-free acetalphosphatides are obtained. The aqueous soln. of the acetalphosphatides is alkaline and gives a strong positive plasmal reaction. 10 g. of the acetalphosphatides are refluxed for 11/2 hrs. with 15 vols. of 10% by vol. methyl alcoholic H2SO4, and the dimethylacetal is extracted with ether-petroleum ether (1:1). The ether-petroleum ether extract is washed, dried and evaporated, the residue purified by treatment with acetone and N/10 alcoholic NaOH, and 3.5-4 g. of dimethylacetal (C18H24(OCH3)2) are obtained. A freshly prepared acetic acid soln. of the dimethylacetal gives the plasmal reaction slowly, but after the soln. has stood 12 hrs., the reaction is strongly positive. When the dimethylacetal is heated to a high temp., it appears to polymerize. When 0.5 g. of the dimethylacetal is dissolved in 10 ml. acetic acid and the soln. kept at 50[degree] overnight, the free aldehyde is obtained, which is then converted to the oxime. The oxime is recrystallized from methyl alcohol, and a difficultly soluble solid (m. p. 84[degree]) and a liquid fraction are obtained. The solid material is shown to be the oxime of stearic aldehyde (C18H37NO). The liquid fraction has not been identified.