Ionizing radiation induces injury to cell membranes resulting in an increase of plasma amino acids concentration and catabolic response of the body. Essential phospholipids (EPL) administered before radiation protect the cell structures and can be used for their renewal. For this reason EPL are expected to have some effect on amino acid metabolism in radiation sickness. The adult male Wistar rats were injected with EPL in a dose of 125 mg EPL/kg b.w. (Essentiale) or saline solution. Three h later whole-body gamma irradiation with a single dose of 10 Gy was performed. Untreated pair-fed rats served as control. The rats were sacrificed 2 days after irradiation. In irradiated rats a decrease in body weight, increased concentrations of plasma amino acids, higher oxidation of branched chain keto acids in liver mitochondria, higher incorporation of leucine into liver proteins and decreased leucine incorporation into proteins of small intestine were observed. In EPL pretreated rats a longer survival time, a higher body weight, lower levels of plasma amino acids and higher protein synthesis in small intestine and in liver when compared with irradiated, saline treated rats were found. No significant changes were observed in branched chain amino acid oxidation measured by means of labeled ketoisocaproate in liver mitochondria.