The results of the studies show that Genetically Engineered Microorganisms (GEM) have the potential to survive, to transfer their novel genetic information, and to affect some microbe-mediated ecological processes in soil. The magnitude of these phenomena in soil in situ, however, is not known and can not be accurately predicted from studies in these simple microcosms. Moreover, some of these studies were conducted with bacteria that are not normal inhabitants of soil, with innocuous novel genes, and with the addition of appropriate recipients. Consequently, more studies need to be conducted with more realistic GEMs in larger microcosms and, eventually, in the field. Until then, the results of these studies should be viewed as being only qualitative indicators of the potential of GEMs in one natural habitat.