The influence of aluminum on the growth and mineral nutrition oftwo ectomycorrhizal fungi, Cantharellus cibarius and Pisolithus sp. was studied in vitro. The mycelial biomass of both fungi decreased as the concentration ofAl increased in the culture medium but C. cibarius wasmore resistant than Pisolithus sp. This growth inhibition was associated with impaired mineral nutrition. Increasing exogenous Al concentration causes Al accumulation in Pisolithus sp., up to 40 mg g-1 dry weight. Aluminum accumulation was much less with C. cibarius.Exogenous Al concentration only poorly affected Ca, Mg, K and P level in Pisolithus sp. whereas C. cibarius accumulated these elements in response to exogenously supplied Al.The acid phosphatase activity of hyphae increased in the presenceof Al in both fungi suggesting a role of these enzymes in Al detoxification. These results are discussed by reference to the possible use of ectomycorrhizal fungi to improve host plant resistance to Al toxicity.