A new phospholipid was detected in the infarcted areas of canine myocardium 24 h after ligation of the left descending branch of the coronary artery. Both the central and peripheral areas of the infarct contained significant amounts of this lipid (4-6& of lipid phosphorus), but it was not present in the apparently normal portions of the same tissue. The lipid was isolated and characterized by its infrared spectrum, by chemical degradation and by comparison with synthetic and semi-synthetic standards. It was identified as a mixture of N-acylethanolamine glycerophospholipids consisting of diacyl-, alk-1-enylacyl- and alkylacylglycerol species. The N-acyl groups were mainly 16 : 0 and 18 : 0 with smaller proportions of 18 : 1 and 18 : 2. The relative decrease of ethanolamine glycerophospholipids in the infarcated areas and the similarity in their molecular species suggests a percursor-product relationship between these phospholipids.