The objective of (Ins study was to assess the effects of the dietary antioxidant supplementation on adrenal glands in Japanese quails (Coturnix coturnix japonica) reared under heat stress using morphometric techniques. A total of 250 (quails. 21 days old. were reared under heat stress (night temperature: 24 degrees C and day temperature: 34 degrees C) and divided into 5 equal groups composed of 30 females and 20 males each according to the dietary regimen: the control group was not supplemented whereas lipoic acid. vitamin C. vitamin E. and vitamin E + vitamin C were daily mixed to the basal starter and grower diets at the dose or 250 mg/kg in the 4 other groups for 21 days. After slaughtering. adrenal glands were examined for morphometric histology. Although the proportions of the different zones of the adrenal tissues have varied according to the sex (males generally exhibited larger zones) and to the dietary treatment. it was observed that the hyperplasia of the cortical tissue induced by heat stress. particularly of the fasciculate and reticular zones. was markedly reduced when birds were supplemented with antioxidants. Treatments with the vitamin E or vitamin C (especially in males) used alone appeared to he the most efficient. whereas the proportions of the medulla zone were significantly increased when quails were supplemented with vitamin C alone or coupled to the vitamin E. These results suggest that a dietary antioxidant supplementation may alleviate the deleterious effects of heat stress by limiting steroid synthesis in the fasciculate and reticular zones in quails.