A survey was made of fungi forming ectomycorrhizas with Betula pendula Roth, and B. pubescens Ehrh. on zinc-contaminated mine tailings. Strains of Paxillus involutus Fr. from toxic and non-toxic soils were compared. There was no indication of fungal adaptation to zinc at either the inter- or intraspecific level. Most of the typical fungal associates of Betula on normal soils were also found on the zinc-rich soils. The ability of different strains of P. involutus to (a) grow in pure culture on agar, (b) form ectomycorrhizas with Betula, and (c) produce a beneficial growth and zinc uptake response in the associated plant, all in the presence of raised zinc concentrations, was not related to the zinc status of the provenance. The ameliorating influence of P. involutus on zinc toxicity to Betula seemed to be positively linked to the degree of compatibility between fungal strain and higher plant.