To investigate similarities between symbiotic interactions of broad bean (Vicia faba) with rhizobia and mycorrhizal fungi, plant gene expression induced by both microsymbionts was compared. We demonstrated the exclusive expression of 19 broad bean genes, including VfENOD2, VfENOD5, VfENOD12 and three different leghemoglobin genes, in root nodules. In contrast, the leghemoglobin gene VfLb29 was found to be induced not only in root nodules, but also in broad bean roots colonized by the mycorrhizal fungus Glomus fasciculatum. In uninfected roots, none of the 20 nodulin transcripts investigated was detectable. VfLb29 has an unusually low sequence homology with all other broad bean leghemoglobins as well as with leghemoglobins from other legumes. It can be regarded as a novel kind of leghemoglobin gene not described until now and the induction of which is common to symbiotic interactions of broad bean with both Rhizobium and a mycorrhizal fungus.