Because of the special importance of saliva in the field of dentistry, we have discussed the relation between the dry mouth and the reduction of salivary flow rate. We have indicated in this study the adverse effects of smoking on the salivary glands and the relation between smoking and the dry mouth, on one hand, and salivery flow rate on the ather. We have also referred to some cases in which the indivedual feels the dryness of the mouth in spite of the possibility of measuring salivary flow rate easily.