We have analyzed the myocardial lipids of an infant with glutaric aciduria type II (GAII) who died from sudden cardiac failure and of five infants who died suddenly from indeterminate causes (sudden infant death syndrome, SIDS). Histology of the SIDS hearts was normal, but there was marked fatty deposition in the GAII heart. Fatty acid composition of myocardial lipids was determined by thin-layer chromatography-gas-liquid chromatography. Total lipid was elevated 20-fold in the GAII heart. Of total fatty acids, 75% was derived from phospholipids in SIDS heart and 89% from neutral lipids in GAII heart. Increased levels of free oleic acid and a 6-fold elevation in the (n-6)/(n-3) fatty acid ratio in phospholipid were noted in GAII heart compared to SIDS hearts.