Symbiont bacteroids were found in the cytoplasm ofSciara ocellariseggs. At the posterior pole of the eggs symbiont agregates are seen from oviposition up to the stage of pole cells formation. These agregates disappear at later stages and the symbionts are included in the two formed pole cells. In somatic regions the symbionts, which were scattered throughout the cytoplam, start to aggregate at the anterior pole of 1 h embryos and there remain up to 2.5 h of development. At later stages the aggregates disappear and the symbionts are once again scattered in the egg endoplasm. Analysis of germ cells during gonadal development in embryonary life (30 and 96 h) and in developed ovary of later 4th instar larva, has showed that the symbionts persist in the germ cells throughout development. No symbionts were found in somatic cells at germ band stage (30 h) as well as at later stages. These findings indicate a transovarian mode of transmission of the symbiont bacteroids inSciara.