The delta-endotoxin gene (tox) from Bacillus thuringiensis subsp. kurstaki HD-1 was cloned into Tn5 and the resulting Tn5-tox element transposed from a vector plasmid into the chromosome of six corn-root-colonizing strains of Pseudomonas fluorescens and Agrobacterium radiobacter. Chromosomal integration of the tox gene maximized stability and minimized the potential for horizontal transfer of the tox gene to other bacterial species. Expression of the tox gene was demonstrated by Western blot analysis and by toxicity against larvae of the tobacco hornworm (Manduca sexta). The method described illustrates how a given gene can be stably integrated into the chromosome of diverse bacterial species.