In one experimental series, 19 rats were fed a nutritionally adequate diet (20% protein) and 19 rats a protein-deficient diet (5% protein). After 18 days, pilocarpine/isoproterenol-stimulated saliva was collected. Saliva from the protein-deficient rats had a lower protein concentration and bacteria agglutinating activity. Calcium concentration was increased. No difference in secretion rate was observed. In another experimental series, 14 rats were given the adequate diet and 14 rats the protein-deficient diet. To enhance biosynthesis in the secretory cells the cells were emptied by an injection of pilocarpine. 1 h later, 14C-glucosamine (UL) was given. After another 2-hour period and after a second stimulation with pilocarpine, saliva was collected. The saliva samples containing radiolabelled glycoproteins were incubated with a serotype c strain of Streptococcus mutans at 37 °C for 30 min to adsorb labelled glycoproteins from the saliva. The total counts in the saliva samples from the two dietary groups were similar, but saliva from the deficient rats contained a lower amount of labelled glycoproteins adsorbable to the bacteria. We conclude that the total amount of glycoprotein synthetized during the experimental 2-hour period is not changed whereas the synthesis of biologically active agglutinin is decreased.