Groups of broiler chickens were fed rations containing .625, 1.25, or 2.5 micrograms total aflatoxin/g of feed from one day to 42 days of age. Treatment groups were segregated according to sex and control groups were maintained. The chickens were bled at 14-day intervals, and serum was collected for assay of total complement (C) activity using a radial hemolytic procedure. No significant differences were found in C titers between males and females of the same age group. For the sexes combined, mean C titers of chickens fed aflatoxin were compared to mean titers of controls. For each age group, significant differences in C titers existed only between the control group and those chickens fed 2.5 micrograms/g aflatoxin. Complement is a major component of the humoral immune response and this study adds to the evidence that aflatoxin can be immunosuppressive to chickens.