Two lines of Japanese quail (AR2.5 and AR3) selected for resistance to aflatoxin and a nonselected control line (NS) were fed diets containing 0, 10, and 20 µg of aflatoxin/g of feed. Line-related reductions in mortality and growth inhibition clearly demonstrated the resistance of the AR lines to dietary aflatoxin. Two-week cumulative mortality percentages for the NS, AR2.5, and AR3 lines fed the 10 µg/g diet were 13.9, 7.7, and 2.6%, respectively, and 44.4, 17.9, and 12.8% at 20 µg/g. Average growth reduction percentages resulting from feeding the 10 and 20 µg/g diets to the NS, AR2.5, and AR3 lines were: 17.3 and 27.5%, 10.7 and 20.1%, and 4.3 and 10.5%, respectively. In addition, AR quail were resistant in varying degrees to the following elevated hepatic b-glucuronidase activity, bursal regression, and hypoproteinemia. Comparisons of the AR and NS lines fed the control diet revealed no detrimental physiological or biochemical response to selection for aflatoxin resistance. Genetic resistance to aflatoxin was associated with increased relative liver weight, higher liver protein content, and elevated plasma concentrations of protein and lipid compared with NS quail. One or more of these differences may be related to the mechanism of genetic resistance to aflatoxin in AR quail.