Strawberry varieties were grown in a field infected with several races of Phytophthora fragariae and scored for resistance to red core disease caused by this fungus. Field resistance of a variety assessed in this way was not related to its pattern of immunity to specific races of the fungus. Possible mechanisms of field resistance were investigated by examining primary root regeneration and the amount of red steles developed in plants grown in infected soil. The least red steles were found in the roots of 53Q13, a highly field resistant Fragaria virginiana derivative. In the fairly field resistant varieties Crusader, Talisman and Templar, resistance was associated with a high capacity for root regeneration. No explanation was found for the field resistance of Cambridge Favourite. The design of a successful screening technique needs to take account of top growth because no single plant characteristic was universally linked with field resistance.