The development of the structure and function of chemosensory apparatus of the tongue of mature and immature mammals was studied by scanning electron microscopy and in behavioral tests. Heterochronic development of receptors structures of dorsal surface of the tongue was established. At birth the chemoreceptors of body and root of the tongue were relatively mature in morphological aspects (the number of taste buds with pore). Taste pores in buds of anterior part of the tongue were found immediately at birth in mature and at the third week of postnatal period in immature animals. Behavioral tests found functional immaturity of chemosensory structures. Immature pups were able to recognize flavoured solutions only on the 7-10 day of age, and preference-aversion reactions of mature pups appeared to the third day of age. The data obtained are discussed in the respect of different ways of adaptation to food contacts with environment of the pups of mature and immature animals.