Subcutaneously injected stearic acid is uptaken by brain and is further incorporated into membrane lipids (especially myelin). The uptake increases regularly up to 20 hrs. in total membranes as in myelin. In total membranes, there is a decrease between 20 and 24 hrs. followed by a recovery of the previous maximal activity. Moreover, the myelin activity increases up to 3 days, so far. Cerebrosides, isolated from both types of preparations, present an activity regularly increasing; but free fatty acids have a stable specific activity and a decreasing relative activity. The injected labelled stearic acid is directly incorporated into membrane lipids or is metabolized inside brain in longer chains (thus providing arachidic behenic and lignoceric acids) or in acetate units (utilized for synthesis of medium chain fatty acids such as palmitic acid).