Plasmids have been constructed that allow integration by a double recombination event at the thrC locus of the Bacillus subtilis (Bs) chromosome. These plasmids can be used either for construction of merodiploid strains and complementation analysis, or for construction of transcriptional fusions to the Escherichia coli lacZ gene. The plasmids contain an antibiotic (An) marker selectable in Bs, as well as an additional An marker outside of the region that can recombine into the chromosome. When used in conjunction with recipient strains containing a third An marker at their thrC locus, these plasmids allow easy identification of transformants issued from a marker exchange event without additional Campbell-type integration. The existing plasmids used for ectopic integration at the amyE locus have been modified similarly.