The ability of ectomycorrhizal fungal isolates to tolerate imposed water stress in pure culture was examined in 55 isolates of 18 species. Water potential treatments, adjusted with polyethylene glycol, were applied to Petri dish units. These units allowed colony diameter measurements of fungi grown on liquid media. Delayed growth initiation and inhibition of growth rate occurred with increasing water stress. For 87% of the isolates, growth rate was inhibited by the initial water potential treatment applied, leaving only seven isolates where growth increased with initial water potential treatments. No growth was evident under the imposed stress treatments for isolates ofLaccaria bicolor,Laccaria laccata, andLactarius controversus; growth occurred only in the control. Drought tolerant species, demonstrated by an ability to grow at a water potential of −3 MPa, includedBoletus edulis,Cenococcum geophilum,Rhizopogon vinicolor, and five out of eightSuillusspecies. Species intolerant of −1 MPa includedHebeloma crustuliniforme,Laccaria bicolor,Laccaria laccata, andSuillus caerulescens. Fungal drought tolerance was poorly correlated with estimates of annual precipitation for collection locations. Estimates of drought tolerance seems to depend more on fungal classification than on annual precipitation at the site of collection. Reisolation ofLaccaria bicolorincreased growth rate and water stress tolerance when compared with the same fungus prior to reisolation.