The inoculation of 5-month-old pine (Pinus densiflora) seedlings with the pine wood nematode (Bursaphelenchus lignicolus) was made by dropping a water suspension of nematodes on a piece of filter paper inserted in the hypocotyl. The average number of living nematodes recovered from each seedling collected just after inoculation was 61 which was considered the number as an inoculum. At the inoculation sites nematodes directly invaded resin canals, the cambial zone, and the cortex. Anatomical observations on the 6th day after inoculation revealed that nematodes were located in resin canals, the cambial zone, and the cortex of hypocotyls resulting in the destruction and necrosis of parenchyma cells of these tissues. On the 9th day after inoculation, a reduction of oleoresin exudation, as a disease symptom induced by nematode inoculation, was first observed, while the increase in the nematode population also was quite remarkable in apparently affected seedlings. Almost all epithelial cells of hypocotyls and roots were destroyed, while parenchyma cells of the cambium, phloem, and cortex were also affected by the nematode attack. On 12th day after inoculation, the destruction of parenchyma cells in epicotyls was noticed in seedlings showing the symptom of a drooping of the epicotyl tip. On the 18th day after inoculation, discoloration of leaves first appeared, and the population of nematodes in diseased seedlings began to decrease once having reached maximum level. Bacterial cells were observed on the 6th day after inoculation in cavities formed by nematodes in resin canals, the cambial zone, and the cortex, and it became more common for masses of bacteria to occupy such cavities throughout the hypocotyls, roots, and epicotyls as the disease developed.