Electron microscopic analysis of Drosophila melanogaster (w1118) ovarian cells has demonstrated that stressful heat treatment of flies results in the appearance of electron dense granules and large lysosomes in the cytoplasm of ovarian cells, which is not related with the presence of Wolbachia, as these changes are observed in both the infected and uninfected flies. High temperature initiates essential envelope defects and other structural changes of symbiotic bacteria in the cytoplasm of ovarian cells. Some embryos developing from eggs of heat shocked flies die, however, bacteria in the survival embryos retain their typical morphology. Endosymbionts do not change their localization and their contacts with the mitochondria and endoplasmic reticulum in the ovarian cells and early embryos after heat shock treatment of the flies. The results obtained show that high temperature influences on both the host and the endosymbiont, but does not change their structural mutual interactions.