• Saliva plays an important role in most biologic events cciuring in the oral cavity and contributes to the mainte nance of systemic health. Secretion occurs in response to a salivary reflex. During the fasting period, mouth dryness con trols basal secretion. Chewing is the main stimulus for secre tion. In human, salivary secretion can be influenced by light/ darkness and other environmental stimuli. Postganglionic fibers originated in the superior cervical ganglia provide sympathetic innervation to salivary and pineal glands. Postsynaptic a-and j3-adrenoceptors mediate salivary re sponses, including synthesis, storage and release of proteins. In mammals, the suprachiasmatic nuclei generate and syn chronize endogenous circadian rhythms and the sympathetic nervous system plays an important role in the propagation of circadian signals. In immature rats, parotid a-amylase and total soluble protein circadian rhythms are controlled by periodic factors whose timing is independent of that imposed by nocturnal chewing of solid food. In rats exposed to various environmental stimuli, such as photoperiod, constant dark ness or light, the submandibular secretory response and fine structure of parotid gland, suggest'that both presence and absence of light can induce adrenergic responses. Homeostatic mechanisms would be required for a differential cow