Polyclonal antibodies (lgG) produced against soluble proteins from spores of Gigaspora rosea showed high specificity with homologous antigens from Gig. rosea in DIBA and ELISA. Fungal species from genera other than Gigaspora were not recognized by the antibodies, nor was Gig. candida whilst the closely related species Gig. margarita showed a weak reaction. Polyclonal antibodies against Gig. rosea tested by immunoblotting of PAGE-separated proteins showed some homology exists in antigens between Gig. rosea and Gig. margarita. Light microscope immunocytochemistry on root sections infected by different arbuscular mycorrhizal fungi not only confirmed the specificity of the antibodies towards Gig. rosea, but also showed that hyphae of Gig. rosea could be distinguished in mixed infections in the same root. The use of soluble proteins as immunogen increases polyclonal antibody specificity so that they can be a reliable molecular marker for identifying a mycorrhizal fungus directly in planta and for studying mycelium distribution in relation to other fungi within roots.