There was a strong correlation (P<0.001) between measurements of red core disease of strawberry, assessed as percentage lengths of the adventitious roots with red steles, and ELISA values obtained from the same root system using a polyclonal antiserum raised to Phytophthora fragariae. ELISA grouped 12 host cultivars/pathogen isolates into 3 categories (highly resistant, partially resistant and susceptible) which agreed with disease incidence after inoculation.