The aim of the study was to determine the influence of the addition for 6 weeks of 12 ppm lycopene (Lyc), 2% fish oil (FO) and/or 0.25 ppm Se as selenate (Se^VI) or selenized yeast (SeY) to an isoenergetic and isonitrogenous basal ration containing sunflower oil (SO) as the source of energy on the liveweight (LW) and feed intake per kg body weight gain of pullets and cockerels. The effects of these additives on the concentrations of fatty acids (FA), especially mono- (MUFA) and polyunsaturated (PUFA) acids, and the yield of PUFA peroxidation (oxidative stress) in breast muscles of chickens were also investigated. Feeding broilers with the experimental rations slightly increased the live body weight of chickens compared with the controls. The ration containing SeY, Lyc, and FO most effectively increased the LW of cockerels, while that of pullets was most efficiently increased by the ration enriched in SeY and Lyc, irrespective of the presence of extra FO. SeY in the ration with Lyc most efficiently elevated feed conversion efficiency (FCE), while Se^VI in the ration containing Lyc most effectively decreased FCE. The addition of Se^VI to the ration enriched in Lyc significantly elevated the sum of saturated fatty acids (SFA), MUFA, and PUFA in muscles of pullets and, especially, cockerels in comparison with all other examined groups. In contrast, FO added to the ration containing Lyc, irrespective of the presence of Se^VI or SeY, decreased the muscle sum of SFA, MUFA, and PUFA, and increased the concentration of docosahexaenoic acid in muscles of chickens compared with the control and all other experimental groups. FO added to the ration, regardless of the presence of Se^VI or SeY, elevated the value of the long-chain n-3 PUFAto- SFA ratio and significantly decreased the values of the n-6 PUFA/n-3 PUFA ratio in muscles of pullets and cockerels. The ration containing Lyc and Se^VI most efficiently increased the value of the PUFA/SFA ratio in the muscles of pullets and, especially, cockerels. The ration containing FO and Lyc most significantly increased the accumulation of malondialdehyde (MDA) in muscles of pullets and, in particular, cockerels, while addition of Se^VI or SeY to the ration enriched in FO and Lyc most considerably decreased the concentration of MDA in breast muscles compared with the control and all other experimental groups. We propose an MDA index (calculated as: MDAindex = (MDA+PUFA)/ PUFA) as an original indicator of PUFA peroxidation in tissues of living organisms. Our results of feeding diets with Lyc, FO, and Se as Se^VI or SeY constitute useful information for nutritionists carrying out investigations to improve chicken performance and the nutritional quality of feed, as well as to improve the nutritive value of chicken meat from the aspect of human health.