Rates of protein synthesis in the major salivary glands of the rat were accurately determined in vivo using the 'flooding dose' technique and the effects of reflex stimulation through feeding or acute ethanol treatment were assessed. Rats were divided into three groups. The control group was fasted overnight, the re-fed group was also fasted then re-fed the following morning and the third group received an intraperitoneal injection of ethanol after an overnight fast. In control rats the sublingual gland had a higher rate of protein synthesis than the other glands. After a feed the rate of protein synthesis in parotid glands was approximately double that of controls whilst that of the submandibular glands had increased by 24% and the sublingual glands remained unchanged. Acute ethanol injection led to a reduced rate of protein synthesis in all glands. The higher rate of protein synthesis in sublingual glands under fasting conditions may be related to the spontaneous secretion of fluid and protein from this gland, which would require a constant replenishment of secretory protein by synthesis. Protein synthesis in the parotid gland, like secretion, appears to be closely linked with the reflex stimulation caused by mastication. The smaller increase in rate of protein synthesis seen in the submandibular gland after a re-feed does not appear to have been recorded before. It could be mediated by the increased reflex stimuli caused by mastication or by some circulating factor. The mechanism by which ethanol reduces protein synthesis in all glands is uncertain.