Seedlings of the annual grass Vulpia ciliata ssp. ambigua were grown in sterilized sand with a dark septate root fungus, Phialophora graminicola, which had been isolated from a natural population of the grass. Tiller number and shoot, root and total biomass of seedlings grown with P. graminicola were enhanced relative to uninoculated control plants in a growth room and a glasshouse experiment. Root length of seedlings grown with P. graminicola was significantly increased, but no effects of the fungus on root diameter, number of root hairs or specific root length were recorded. Root nitrogen content and shoot, root and total phosphorus contents of seedlings grown with the fungus were enhanced, but shoot nitrogen concentration of these plants was reduced. Shoot biomass and specific root length of inoculated plants were positively associated with the number of P. graminicola colonies re-isolated from roots. These data indicate that P. graminicola acts as a beneficial associate of V. ciliata ssp. ambigua seedlings under controlled conditions.