By means of quantitative morphological analysis tissue basophils (TB) (mast cells) in the derm and in the subcutaneous loose connective tissue have been studied at various degree of thermal lesion of the skin. Average diameter, amount of the cells per 0.1 mm2 of the slice area and distance between them serve as criteria for estimation of the TB functional activity. Certain differences have been revealed in the TB state at a weak and severe thermal lesion of the skin. At a threshold thermal action, metabolic processes in the TB become active. Burns of the skin of the II and IIIa degree result in an increased discharge of the granular component from cytoplasm and often in death of the cells. By means of multiple linear regression equations certain dependence of the degree of the thermal skin lesion on the state of the TB population in various dermal layers and in the subcutaneous loose connective tissue is stated.