Abstract: The present study was aimed at elucidating the morphological variations of Indonesian isolates of Cochliobolus heterostrophus (Drechsler) Drechsler as well as exploring pathogenicity of the isolates. Potential specificity between host varieties and pathogen isolates in the corn–southern leaf blight pathosystem was also exploited. Isolates of C. heterostrophus were collected from ecologically different parts of the country including the islands of Bali, Java, Sulawesi and Sumatera. Variations in morphological and pathogenic characteristics were observed among the isolates although possible host specificity was unlikely to exist between the corn varieties and fungal isolates tested. These results suggested that agricultural ecosystems might have affected morphological and pathological variations within Indonesian isolates of the fungus provided the existence of a common ancestor of the isolates.