The effect of dietary conjugated linoleic acid (CLA) on body composition and energy metabolism was investigated in broiler chickens. Male broiler chicks were assigned to receive either a control diet (1 % sunflower oil) or a diet containing CLA (1 % of a 1:1 mixture of trans-10, cis-12 and cis-9, trans-11 isomers of octadecadienoic acid). The diets were fed ad libitum for 3 weeks and there were eight replicates per diet, each replicate including four chickens so that each treatment had thirty-two animals. The proportion of body fat was lower in the control group than in the CLA group. No significant differences as to the proportions of body water, ash and protein were observed. Feed and energy intake were significantly lower in CLA-fed birds. The percentage of ingested energy lost in excreta was higher after CLA feeding and heat expenditure as a percentage of ingested energy was lower in the CLA-fed group. The CLA-fed group showed a higher percentage of SFA and lower percentages of MUFA and PUFA in carcass fat. It is concluded that CLA stimulated de novo fatty acid synthesis and lowered desaturase activity.