Abstract - We tested the hypothesis that a low protein diet (5%) would change the conditions for synthesis and release of protein from the salivary secretory cells and increase caries development. In addition, we tested whether the simultaneous use of a β-adrenoceptor agonist or antagonist had an additive effect. After an experimental period of nine weeks the animals led the 5% protein diet had lower body weights, saliva secretion rates and total protein secreted per minute than a control group fed a 20% protein diet. There were greater numbers of cariogenic streptococci on the teeth and the caries scores were higher in the rats fed the low protein diet than in the rats in the control group. The β-receptor agonist, isoproterenol, given to rats fed the 20% protein diet, caused a reduction in protein concentration and amylase activity in saliva and a slight increase in caries development. Propranolol had no effect on cither saliva composition or caries development.