Release of genetically engineered organisms into the environment pose qualitatively new ecological risks of global dimensions because they are potentially irreversible. At this point in time, the implications of these releases cannot be properly assessed on the basis of scientific knowledge developed in the fields of microbiology or evolutionary ecology. This is especially true for long-term evolutionary effects. Therefore, the only sound scientific approach is a strict application of the precautionary principle. This approach is further validated by the fact that present applications of genetically engineered crops, as well as the circumstances of their introduction to the market, cast substantial doubts about the agricultural concepts on which they are based. To some extent, the necessary development of sustainable and ultimately organic agricultural practices is thwarted, if not actively attacked, by the false promises and untenable choices induced by genetic engineering in agriculture.