Three dietary inclusion rates of CLA (0, 2 and 4 g/kg feed) and aflatoxin B, (0, 200 and 300 mu g/kg feed) were tested in a 3 x 3 factorial experimental design on a total of 99 Ross-308 male broiler chickens from 1 to 42 days of age. The objective of this study was to determine the effect of dietary conjugated linoleic acid (CLA) on carcass characteristics, serum lipid variables and histopathological properties in broiler chickens receiving a diet containing aflatoxin B-1 (AFB(1)). Carcass yield, abdominal fat weight and abdominal fat percentage were not significantly influenced by dietary CLA, AFB(1) or CLA + AFB(1). Altered serum lipid measurements induced by AFB, treatments included increased serum cholesterol and triglyceride concentrations, and decreased serum concentration of high density lipoprotein (HDL). Serum HDL concentration was increased in birds supplemented with 2 and 4 g CLA/kg diet compared with the control group. However, CLA + AFB, did not significantly affect these parameters compared to the groups that received AFB, alone. Aflatoxin B, administration induced degenerative changes in the liver tissue, but dietary CLA supplementation offered protection to the livers against these changes. Aflatoxin B, residues were not detected in any breast tissues collected from the broiler carcasses. Our results suggest that CLA provided protection against the negative effects of liver damage induced by AFB, in broiler chickens. Furthermore, dietary CLA supplementation increased serum HDL levels.