Sixty 1-day-old male Ross-PM3 broiler chickens were used in this study. The chickens were divided into 5 groups, including one control and 4 experimental. The control group was fed commercial broiler feed free from aflatoxin (AF), whereas the experimental groups, namely, groups 2, 3, 4 and 5 were given feed containing, respectively, 0.05 ppm, 0.1 ppm, 0.5 ppm and 1.0 ppm of AF (approximately, 81.30% AF B-1, 10.40% AF B-2, 5.75% AF G(1) and 2.55% AF G(2)) for 45 days. Blood samples were collected on days 15, 30 and 45 of the study. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glucose-6-phosphate dehydrogenase (G6PD) activity and malondialdehyde (MDA) levels in erythrocytes were determined. The results of this study revealed a significant decline in comparison to the control group with respect to SOD activity on days 30 and 45 in groups 4 and 5, GSH-Px activity on day 30 in group 5 and day 45 in groups 4 and 5. CAT activity on day 45 in group 5 and G6PD activity on day 45 in group 5, and a significant increase in the level of MDA in group 5. Therefore it was concluded that long-term (30 and 45 days) administration of AF at high doses (0.5-1.0 ppm) caused lipid peroxidation in broiler chickens. Certain significant statistical changes that occurred on day 30 in SOD and GSH-Px activities, and on day 45 in primarily SOD and GSH-Px (for groups 4 and 5) and secondly (for group 5) in all enzyme activities and MDA levels are supportive of this hypothesis. Furthermore, it has been understood that the most sensitive parameters utilised in determination of lipid peroxidation may include SOD, GSH-Px and MDA, and these parameters may prove to be significant with regard to the assessment of the severity of aflatoxicosis in poultry naturally intoxicated with AF, implementation of precautions taken against AF intoxication and the evaluation of such practices with regard to success.