The submandibular salivary gland was histochemically and electron microscopically studied in gnotobiotic and conventional Wistar rats at the age of 15 days--10 months. By the first month of age, the submandibular salivary glands in both groups of animals complete differentiation of their acini, and the gland, according to the type of its secretion, becomes seromucous with predominance of albuminous component in it. Succinate dehydrogenase activity and nonspecific esterase predominate in epithelium of the excretory ducts. At the second month of life some signs of moreasing ductal part of the gland appear in the gnotobiotic rats. This part greatly increases by the 4th--10th month of life, mainly at the expense of twisted granular sections. This increase in number and volume of the twisted granular ducts results in compressing acini and in ultrastructural disorders of granulocytes, with destruction of some mitochondria, increasing number of lysosomes, decreasing size and alterations in character of secretory granules, in structural disorders of the laminar complex. All these manifest depressing secretory function of granulocytes in the gland of gnotobiotic animals.