Unsaturated soil columns were used to examine the transport of the plasmid pLEPO1 and plant DNA (transplastomic tobacco DNA), both carrying an antibiotic resistance gene (aadA gene), and the capacity of bacteria to incorporate the gene in their genome after its passage through the soil. Soil columns containing a top leaf layer had sterile water percolated through them at a rate of 0.5 mL h(-1). DNA from column leachate water was extracted and analyzed. Quantitative measurements included total DNA concentrations in the water and the transformation frequencies of Acinetobacter sp. BD413 by DNA in the column effluent. Qualitative measurements included the relative degradation of DNA after passage in the columns by agarose gel electrophoresis and the potential of effluent DNA to transform bacteria, leading to the production of anti biotic-resistant bacteria. The presence of aadA gene in the leachate water of soil columns suggests the mobility of DNA in unsaturated soil medium. The extent of DNA degradation was found to be proportional to its residence time in the soil column while a fraction of DNA was always able to incorporate into the Acinetobacter genome under all conditions studied. These results suggest that biologically active transgenic DNA might be transported downward by rain in unsaturated soils.