Transmission electron microscopy studies showed many bacteria associated with the sporocarps of Glomus mosseae, occurring not only on the hyphal surface, but also on the surface of spores within the sporocarps and in microniches formed by peridial hyphae. Sequential cuts of the sporocarps showed the spatial distribution of the bacteria, and evidenced bacterial cells embedded in spore walls by means of tunnels mined within the electron-dense spore wall layers. Quantitative determinations of microorganisms associated with G. mosseae sporocarps showed the occurrence of large numbers of bacteria, fungi and actinomycetes on the sporocarp surface and in the sporocarp homogenate. Moreover, chitinolytic microbes were detected in the sporocarps.