The distribution and concentration of lipid components of different media used for organotypic cultures of rat brain cortex have been measured quantitatively. Five cholesterol ester species have been fractionated from chicken embryonic extract. Their fatty acid profiles have been determined by combined gas liquid chromatography-mass spectrometry. The depletion characteristics of medium cholesterol esters and some fatty acids during development of brain cortex were not symmetrical. Polyunsaturated fatty acids of the medium were lowered prior to the saturated and monoenoic fatty acids. The phenomenon of depletion may be correlated with enhanced esterase activity mediated by the tissue.