Reports made over the past few years leave little doubt that horizontal gene transfer among bacteria can and does occur in the environment. The significance of these events in the dissemination of recombinant molecules is not clear and more research is required to fully appreciate the impact of genetic exchange on their stability and survival. Based on the available data it is fair to say that horizontal gene transfer may play as important a role in transmission of recombinant sequences as does the survival and persistence of genetically engineered microorganisms.