In recent years, dieback of durian has become a major problem in mature orchards in the northern Queensland wet tropics region. A survey of 13 durian orchards was conducted during the dry season (July–September 2001) and following wet season (February–April 2002), with roots and soil from the root zone of affected trees being sampled. Phytophthora palmivora was recovered from the roots of affected trees on 12 of the 13 farms in the dry season, and all farms in the wet season. Pythium vexans was recovered from all 13 farms in both seasons. P. palmivora and P. vexans were recovered from diseased roots of 3-month-old durian seedlings cv. Monthong artificially inoculated with these organisms.