Three species of ectomycorrhizal fungi (Hebeloma crustuliniforme, Sufflus variegatus and Cenococcum geophilum) were grown in axenic culture amended with range of AsO43- concentration under three different PO43- regimes. The fungi exhibited different growth responses to AsO43- that varied with PO43- concentration. Suillus variegatus showed the greatest sensitivity to AsO43-, with growth almost completely inhibited in the presence of AsO43- under the lower two PO43- treatments. Under the highest PO43- treatment however, growth was enhanced and S. variegatus was able to persist at AsO43- concentrations of up to 4 mM. Hebeloma crustuliniforme also showed high sensitivity to AsO43- especially at low PO43- concentration. The two higher PO43- treatments had an ameliorating effect on AsO43- toxicity in H. crustuliniforme. This demonstrates the ability of PO43- toxicity to alleviate AsO43-. The response from S. variegatus and H. crustuliniforme, both basidiomycetes, was in contrast to the ascomycete C. geophilum. This fungus demonstrated tolerance to AsO43- when grown in culture solution and PO43- did not have an ameliorating effect on AsO43- toxicity in C. geophilum.