Inoculation techniques have suggested that some European Chestnut, Castanea sativa, are resistant to Phytophthora cinnamomi, fungus most frequently associated with chestnut ink disease. This paper reports a new inoculation method for assessing resistance of chestnuts to P. cinnamomi. Mycelium was inoculated in excided chestnut stems, when plant annual growth was approximately 30-40 cm long. Stems were incubated in suitable temperature and humidity conditions and the lesion extension was measured. This method allows the assessment of mature trees resistance and a quick testing of large amounts of plants. Besides, it is easy to undertake and makes the selection criteria more objective. Based on morphological and biochemical criteria, different isolates of Phytophthora were studied as well. Difficulties in obtaining all the morphological characters to identify the species of Phytophthora were overcome by the analysis of proteic and enzymatic profiles of mycelial proteins on acrylamide gel electrophoresis.