The ability ofBacillusspp. to alter the nodulation ofPhaseolus vulgarisbyRhizobium etliwas assessed. The simultaneous presence of bothRhizobium etliTAL 182 andBacillus megateriumS49 on plant roots during the early stages of plant growth was necessary for enhanced nodulation ofPhaseolus vulgarisby theRhizobiummicrosymbiont. Coinoculation with both bacterial species also facilitated heterologous nodulation ofRhizobiumTAL 182 onPhaseolus acutifolius. These results are consistent with earlier reports of increased root hair proliferation and lateral root formation in response to coinoculation. Split-root experiments revealed that coinoculation partially suppressed host-controlled regulation of nodulation, implicating a plant interaction with the two bacterial species. Changes to the nodulation potential ofR.etlidue to coinoculation withBacillusspp. demonstrate the potential for root-associated organisms other than rhizobia to alter the dynamics of the legume–Rhizobiumsymbiosis.Key words:Bacillus, nodulation enhancement, heterologous nodulation.