In March 1999, we measured the number of bacteria in the soil where Pinus thunbergii grew on the scoriae accumulated at volcano eruptions at Miyake-Jima, Izu Islands, Japan. The number of bacteria was high on the surface of ectomycorrhizae of P. thunbergii and in mycosphere soil of ectomycorrhizal fungi associated with this tree. Capacity of Alnus sieboldiana nodulation and of ectomycorrhizal formation of A. sieboldiana- and P. thunbergii seedlings were also compared in the soils where these plants grew in this site. Nodulation capacity of A. sieboldiana was high in rhizosphere of A. sieboldiana and low in the mycosphere of ectomycorrhizal fungi of pine. No nodulation was observed in non-mycosphere soil of this site. Abundant mycorrhizae were formed on alder seedlings cultivated in rhizosphere of the alder and on pine seedlings cultivated in mycosphere soil of ectomycorrhizal fungi of the pine. No ectomycorrhizae were formed in pine and alder seedlings cultivated in non-mycosphere soil.