Electron microscopical changes in the renal morphofunctional units were studied during the first minutes after termal trauma in the experiments performed with mongrel male dogs. The glomeruli were demonstrated to have some evidence of glomerulonephritis, particularly, in the capillaries of those glomeruli where local thickening of the basal membrane was most constant and where endothelium and podocytes, i. e. the structures directly participating in filtration were involved in the process. Proximal areas of nephrons had a peculiar compact mitochondrial matrix, disturbed basal-apical mitochondrial orientation, shortening of plasmolemma folds, increase in cytosomal number. Activation in the latter was accompanied not only with focal degeneration of cytoplasm but with some changes in the cell as a whole with its subsequent squamation into the lumen. In the epithelium of distal parts of the nephrons and collecting tubes, distrophic changes were registered, as well as a reduction in the folds of plasmolemma which was followed by a disturbance in the integrity of the basal labyrinth and mitochondrial swelling. A large amount of vesicular elements were noted in cytoplasm of the cells, the cells were swelled and underwent focal degeneration.