Ethyl esters of long-chain fatty acids are formed in the liver and brain of mice after 1-6 days of ethanol intoxication. This observation extends the reports of Lange and co-workers who detected these compounds as unusual metabolites of ethanol in human tissues [E. A. Laposata and L. G. Lange, Science 231, 497 (1986)]. Ethyl esters of oleic and linoleic acids, and, in smaller amounts, ethyl esters of palmitic and stearic acids were found in the livers of mice that had been treated with ethanol by inhalation. In the brain, only the esters of unsaturated fatty acids were found, in lower amounts than in liver. All the fatty acid ethyl esters seemed to have reached steady-state levels in the tissues after 3 or 4 days of alcohol treatment. When incorporated into synaptosomal plasma membranes in vitro, in intramembrane concentrations estimated to resemble those observed in the mice, these esters reduced the fluorescence anisotropy, i.e. they disordered the membranes.