A phytotoxin produced by the sugarcane red-rot fungus Colletotrichum falcatum Went was partially purified. The phytotoxin caused increased electrolyte leakage in susceptible sugarcane varieties and higher levels of phytoalexins (3-deoxyanthocyanidins) in resistant sugarcane varieties. This relationship between phytotoxin induced changes and disease reaction could possibly be used as an additional index to rapidly identify red-rot resistant varieties.