Brain tissue, both grey and white matter from the cerebral parietal region and the cerebellum, was obtained from 66 infants dying of sudden infant death syndrome. The fatty acid composition was analysed in these tissues by gas liquid chromatography after extraction and derivatisation. The subjects were divided according to their dietary history, either breast or formula feeding. Formula-fed infants were further subdivided according to the content of -linolenic acid in the formula milk. At the time of this study no formula milks analysed contained long chain polyunsaturated fatty acids. Dietary related differences were found in the accretion of polyunsaturated fatty acids into neural membranes. Docosahexaenoic acid concentrations were higher and conversely n-6 series fatty acids lower in breast-fed than formula-fed infants. In cerebral white matter, nervonic acid, the long-chain fatty acid associated with myelination, appeared in breast-fed in advance of formula-fed infants. Similar dietary related differences in polyunsaturated fatty acid compositions were found in the cerebella cortex and the cerebellar white matter was associated with an earlier accretion of nervonic and lignoceric acids when compared to the cerebrum. Analysis of the phospholipid and glycolipid composition of the cerebral and cerebellar white matter tissues was achieved by means of separation by high performance thin layer chromatography followed by scanning densitometry. The results of this study support the need for breast feeding for a minimum of four months. Formulation of manufactured milks should include long chain polyunsaturated fatty acids and nervonic acid at concentrations similar to those of breast milk.