Content of total lipids, phospholipids and total protein was decreased in rat brain synaptic membranes during autolysis within 1 h and 24 hrs at 37 degrees in the medium used for isolation of the membranes. Within early steps of autolysis (1 h), total lipids and phospholipids were only slightly altered, while a decrease in the concentrations of phosphatidyl cholines, phosphatidyl ethanolamines and cholesterol was found simultaneously increased in relation to the content of lysophospholipids, phosphatidyl serines+sphingomyelins, cholesterol esters, triacylglycerols and free fatty acids. Within later periods of autolysis (24 hrs) the further dissimilar decrease was observed in relative content of phosphatidyl cholines, phosphatidyl ethanolamines, phosphatidyl serines+sphingomyelins with synchronous increase in the level of glycerophosphates, lysophospholipids, phosphatidic acid+polyglycerophosphatides, cholesterol esters; occurrence of diacylglycerols was detected. Possible mechanisms (involving hydrolase, transacylase reactions) of alterations observed in lipids from synaptic membranes during autolysis are discussed. Modern experimental technique appears to be useful in order to gain insight into molecular mechanisms of brain death and the postmortal loss of information.