Results are presented from several aspects of 30 years'' studies on Pyricularia oryzae. These include techniques developed for production of dry spore inocula and evaluation of pathogenicity and host specificity toward the standard differential rice cultivars after long-term storage of the pathogen in various forms. Induced or natural mutations (or paresexual recombinations) occurred occasionally, usually resulting in broader host range and/or increased sporulating capacity. By far, the majority of > 100 isolates surveyed retained their original pattern of specialization after 20-30 yr in culture with periodic transfer. With respect to the controversy regarding stability of pathogenic races of the rice blast pathogen, the results of our studies strongly support the concept that the species P. oryzae comprises a wide range of pathotypes (races) each characterized by its capacity to attack certain cultivars of rice; that these races are basically stable; and that mutations are the exception rather than the rule.