The purpose of this study was to investigate in the rat heart and liver the effects of an acute administration of three anthracyclines, doxorubicin, epirubicin and pirarubicin, and an anthracenedione, mitoxantrone, on the membrane peroxidative status, which was estimated by the composition of polyunsaturated fatty acids (PUFA), and on the activities of the enzymes involved in membrane repair processes and lipid hydroperoxide detoxification. Rats were injected for four consecutive days with the drugs or saline (control) and killed 24 hr after the last injection. All the drugs induced an increase in plasma thiobarbituric reactive substances and α-tocopherol concentrations, both expressed per milligram of plasma lipids. Plasma vitamin A was decreased by about a factor of two by all the drugs. The fatty acid profile in the heart lipids showed that the polyunsaturated species (20:4 n-6, 22:6 n-3) remained at the same or even higher levels after anthracycline treatment. This can be explained by the fact that the activities of the enzymes involved in either the recycling of membrane phospholipids, such as phospholipases A1 and A2 (EC 22.214.171.124 and EC 126.96.36.199), lysophospholipases (EC 188.8.131.52) and acylCoA:lysophosphatidylcholine acyltransferases (EC 184.108.40.206), or hydroperoxide detoxification, such as selenium-dependent glutathione peroxidase (GSH-PX, EC 220.127.116.11) and glutathione S-transferases (GSH-T, EC 18.104.22.168), were maintained at the same level of activity after the antitumoral treatment. In liver, membrane phospholipid levels of PUFA were maintained as well as the activities of phospholipidmetabolizing enzymes. GSH-PX activity was not affected whereas that of GSH-T was slightly lowered by the drugs. These results suggest that during acute antitumoral-induced lipid peroxidation of membranes, the multi-enzymatic complex of the immediate processes of repair and detoxification is fully operational, allowing the membrane to rapidly recover its functional status. The results are discussed in the context of the equivocal relationships between antitumoral-induced lipid peroxidation and cardiac disturbances.