Pure cerebrosides, sphingomyelines, lecithines and neutral fats were isolated from brains of young rats 6 and 72 hours after intracerebral injection of 14C acetate. We detected the composition of their fatty acids and determined the specific activities. The highest value was always found in palmitic acid which obviously is the precursor for the formation of the other fatty acids. The applied activity incorporated in the fatty acids of lecithines and neutral fats was much higher than the amount concerning cerebrosides and sphingomyelines. Therefore these two lipid fractions showed a much lower turnover.