Favre and coworkers (Favre et al., Biochimie 73:235-244, 1991) previously reported that the Bordetella pertussis recA gene present at high copy number could promote a low frequency of recombination, but not bacteriophage induction in Escherichia coli RecA(-) mutants. Reexamination of these phenotypes demonstrated that, in contrast to the previous study, when this gene is present at high copy number, it can stimulate a 2- to 4-log frequency of bacteriophage induction in the presence of mitomycin C, but no appreciable spontaneous induction. The cloned gene, whether it was present in high or low copy number, also promoted a low frequency of intrachromosomal recombination of two duplicated genes in Escherichia coli. These results suggest that a high concentration of the B. pertussis RecA protein is required to promote high-frequency mitomycin C-stimulated bacteriophage induction, but it facilitates intrachromosomal recombination at a very low frequency in E. coli RecA(-) mutants. The ability of the B. pertussis RecA protein to promote mitomycin C induction and its inability to appreciably stimulate spontaneous induction of bacteriophage suggest that this protein possesses a unique phenotype compared with other RecA proteins.