Critics of agricultural biotechnology have often been dismissed as modern-day Luddites. However, these critics have an understandable concern, based on a detail of the technology that has been nearly unanimously adopted for introducing foreign genes into plants. This method relies on cointroducing, along with the gene to impart a desired characteristic, another gene that confers antibiotic resis-tance. Culturing the transformed cells in antibiotic-containing growth media allows selection and regeneration of only those cells that have incorporated the transgenes. The antibiotic resistance genes used in genetic engineering are, in fact, normal bacterial genes that have been adapted for expression in plants. However, the prospect of releasing these antibiotic resistance genes into the envi-ronment in large quantities has raised fears that they could be taken up by native bacteria, thereby posing a risk to public health. Industry and the FDA have responded to these concerns by asserting that genes that have been transferred into plants cannot be rein-corporated into bacteria 1 .When industry first began making such guarantees in the 1980s, I was exploring the idea (and trying to convince my colleagues) that horizontal gene transfer between king-doms could be a natural process. This idea was based on the numerous demonstrations that bacteria, fungi, and animal cells readily take up and express foreign DNA. I argued that this could reflect natural processes that facilitate horizontal gene transfer. And if this speculation was proven, the debate over the safety of recombinant DNA technology would have to be recast.Since then, research has focused primarily on the question of whether or not the genes in these plants will move to bacteria in the envi-ronment, rather than on whether or not the genes pose any danger if they do move. The FDA assertion that horizontal gene transfer does not occur between transgenic plants and microorganisms has stimulated a number of investigations, centering on two types of experiments, neither of which have provided evidence for such gene transfer. In the first, transgenic plant materials were fed to mice and the coliform bacteria isolated from their feces screened for the presence of antibiotic resis-tance genes originating from the plants. After eight trials, none could be recovered (M. Syvanen, unpublished data). In the second approach, two labs examined bacteria that cause spoilage of vegetables and asked whether, after growth on transgenic plants, the bacteria had been transformed with transgenic DNA. In both cases the bacterium Erwinia chrysan-themum was grown on a variety of vegetables, but no transformants were detected (ref. 2, M. Syvanen, unpublished data).