Five different cultivars of taro and two other related aroids were screened for the induction of pathogenesis-related (PR) proteins in response to infection by Phytophthora colocasiae, the fungal pathogen responsible for taro leaf blight. Extra-cellular fluid from infected leaves was tested for PR protein expression by SDS-PAGE analysis and activity gels were used to measure the activity of the known PR proteins (?-1,3-glucanase, proteinase inhibitors, and peroxidase). Infected plants showed increased levels of PR proteins but this did not correlate with resistance in the most susceptible cultivars. Despite high levels of some PR protein, these cultivars were unable to prevent infection. Successful resistance in other plants was more closely linked to the pattern of expression of proteinase inhibitors which appear to be an important defence strategy in taro and related aroids.