Performance parameters and oxidation of body lipids of broiler chickens were investigated when their diet was supplemented with a commercial preparation of essential oils (Apacox) derived from selected herbs. One hundred and twenty day-old Cobb-500 female chicks were divided into four groups with three replicates each. One group received the basal diet, the control. The three experimental diets consisted of the basal diet to which either 200 mg α–tocopheryl acetate/kg (Toc200 group), Apacox at 0.5 g/kg (Apa0.5 group) or Apacox at 1.0 g/kg diet (Apa1.0 group) was added. At the end of the 42 day feeding period there were no differences in initial and final body weights, daily weight gains, daily feed intakes and feed conversion ratios between treatments, and no mortalities were recorded. It is concluded that the mixture of herbal essential oils exerted no growth-promoting effect when incorporated in the chicken diet. The progress of lipid oxidation was assessed in raw and heat treated breast and thigh muscle at 0, 3, 6 and 9 days of refrigerated storage at 4 oC. Results showed that Apacox retarded lipid oxidation in both raw and heat treated breast and thigh muscles at all time points, with the supplementation level of 1.0 g/kg diet being more effective in retarding lipid oxidation than the 0.5 g Apacox/kg treatment. The retardation offered by Apacox was, however, inferior to that exhibited by α–tocopheryl acetate supplementation. Raw and heat treated thigh muscle samples were more susceptible to oxidation compared to breast muscle, although the latter contained α–tocopherol at markedly lower concentrations.