To further explore the biological mechanism of “kidney corresponding with winter and governing storage”,and the essential connotation of Kidney's Viscera Picture in Traditional Chinese Medicine and the role of pineal gland in the process of seasonal variations by observing and comparing the seasonal variation of the contents of melatonin (MT) in the hypothalamus-pituitary-adrenal axis (HPA axis) of golden hamsters between the normal group and the model group (Pinealectomy) Methods:Hypothalamus,pituitary and adrenal tissue were drawn from golden hamsters on spring equinox,summer solstice,autumn equinox and winter solstice and the contents of melatonin were determined by Enzyme linked immunosorbent assay (ELISA).Results:There was seasonal variation of MT level in the hypothalamus and pituitary tissue of hamsters in normal group; there was significant seasonal variation in the MT level of adrenal tissue in the normal group,while the seasonal rhythmicity of MT level of adrenal disappeared after pineal gland extirpation.The change trend of MT content in hypothalamus of normal group was winter>summer>autumn>spring,and the trend of expression of MT in hypothalamus of model group was summer>autumn>winter>spring.The change trend of MT content in the normal group was summer>spring>winter>autumn,while the content of MT in the model group was>summer>autumn>spring>winter.The change trend of MT content in normal group was winter>summer>autumn>spring,while the content of MT in adrenal gland of model group was>summer>spring>autumn>winter.Conclusion:Melatonin level had a seasonal pattern in various tissues of the hypothalamic-pituitary-adrenal axis; Pineal gland had a direct effect on the seasonal variation of melatonin in the hypothalamus-pituitary-adrenal axis; The level of melatonin in the adrenal gland in winter was higher than that in the other three seasons,indicating that melatonin had the strongest effect on adrenal gland's function in winter.