Macro- and microscopic changes were studied in case of reproduction of the local Schwartzmann phenomenon in animals with various extent of bioisolation. It was revealed that the Schwartzmann phenomenon was positive in the usual animals and negative in the germ-free guinea pigs and in the animals with reduced enteric microbial flora given sterile diet. In the absence of microscopic changes in the germ-free animals there was revealed in their skin a neutrophilic-mononuclear infiltration of the derma, dilatation of the vessels, thrombosis of individual vessels. Apart from the same changes in guinea pigs with a reduced microbial flora, there were found focal extravasation and thrombosis of a somewhat greater number of vessels. There was no marked thromboses of small branches of the vessels, extensive hemorrhages or necroses which usually accompanied positive Schwartzmann phenomenon.