Vasoactive intestinal peptide (VIP) injected intravenously was found to induce a flow of saliva from both the parotid and the submaxillary gland in the rat. The secretion was slow in onset. The amount of saliva secreted from the parotid gland was less than that from the submaxillary gland. Parotid saliva was very viscous. VIP-evoked parotid saliva was more protein rich than both submaxillary saliva and saliva secreted in response to other sialagogue drugs including the β-adrenergic receptor agonist isoprenaline. The effect of VIP was direct; it occurred after removal of the adrenals, after degeneration of intraglandular nerves and in the presence of autonomic blockers. A supersensitivity to VIP was demonstrable. In the parotid and the submaxillary glands the secretory response to VIP was enlarged following parasympathetic denervation and decentralization, respectively, while after sympathetic denervation supersensitivity was only found to develop in the submaxillary gland.