The effect of temperature on pine wilt development in Scots pine (Pinus sylvestris) was examined in three experiments. Container-grown pines (4-6 years old) inoculated with 1,500 Bursaphelenchus xylophilus were incubated at constant temperatures in growth chamber for 8 weeks, then at a temperature range of 15-30 C in a greenhouse for 10-12 weeks. Nematode infection was greater, tree mortality was higher, and disease incubation was shorter at 32 and 30 C than at 25, 23, 18, and 11 C. Foliar symptoms developed more rapidly and uniformly at higher temperatures. Ninety-five percent of tree deaths at 32 and 30 C and 88% at 25 and 23 C occurred within the 8-week exposure to constant temperatures. Mortality at 18, 16, and 11 C occurred only after transfer to the greenhouse. Results indicate that pine wilt incidence is directly related and disease incubation period is inversely related to temperature and that high-temperature stress predisposes Scots pine to lethal infection by B. xylophilus.