The influence of the photo period, of pinealectomy and of bilateral enucleation on several endocrine organ weights of Japanese quail (Coturnix cotumix japonica) have been explored. At 5 weeks after hatching, pituitary, adrenal and gonadal weights were higher, and thyroid weight was lower, in birds maintained under continuous light (24L/OD) than in those held under a short phoroperiod (8L/16D) for 3 weeks. Blinded birds did not differ from sham-pinealectomized ones in these endocrine parameters. Pinealectomy abolished the photoperiod-dependent responses of the adrenal and thyroid, while pituitary and gonadal weights were unaffected. At 6 weeks after hatching, the previously observed thyroid response was not as pronounced, and pinealectomy no longer altered the adrenal response to the photoperiod. Thus, the photoperiod and the pineal appear to be important for maturation of several endocrine glands, and the eyes do not seem to be necessary for these photo-endocrine responses in Japanese quail. (Endocrinolog...