The role of fatty acids in membrane structure is very important; this is particularly true in brain where two highly differentiated membranes are operative: myelin and nerve endings. The former contains 10 times as much long chain sphingolipids as any other known structure: very long chain saturated and mono-unsaturated fatty acids are concentrated in myelin and their presence in the sheath confers to the membrane increased stability. Thus their biosynthesis is a fundamental event during the maturation of the brain and alteration in the activities of enzymes involved in very long chain fatty acids biosynthesis could have a profound effect on the integrity and stability of the myelin membrane.