Causes of mortality of containerized western larch seedlings at the Champion Timberlands Nursery, Plains, Montana, were investigated. Seedlings were rated for disease severity based on extent of foliar decline symptoms and fungal isolations made from their roots. Isolations were also made from selected larch seed. Consistent associations between root colonization by potentially pathogenic fungi and level of disease symptoms were not found. Fusarium spp. were only isolated from a few seeds and seedlings sampled toward the end of the growth cycle. These fungi were also frequently isolated from asymptomatic seedlings. It was concluded that heat injury which occurred during the spring when tissues were sensitive was the most likely cause of seedling mortality.