Fusarium wilt of cotton (Gossypium. spp. ) is caused by the fungus Fusarium oxysporum schletend f.sp vasinfectum (Atk) Snyder and Hansen (Fov). The disease has been recorded in most of the world's major cotton growing areas and causes significant losses in the USA, Tanzania, Egypt, and India (Smith et al 1981) and China (Chen et al, 1985). Australia was considered to be free from the wilt pathogen until 1993, when it was confirmed in Queensland (Kochman, 1995). Fov was also recently discovered in the Philippines. Wilted cotton plants have been collected from field sites throughout the Queensland and New South Wales growing areas since 1993. Several hundred isolates of Fov have been recovered from such material and examined in laboratory and glasshouse studies to determine the range of genetic and pathogenic diversity in the Australian fungal population. Where possible, Australian isolates have also been compared with isolates of Fov imported under quarantine from other countries