Abstract: The larvae of Meloidogyne hapla Chitwood, after entering the tomato root, stimulated the formation of giant cells. These were formed by the enlargement of single cells in which multiple divisions and fusions of nuclei occurred, although coalescence of adjacent cells in early stages of infestation likewise participated in the formation of giant cells. In a later stage, the nuclear-fusion like phenomena became very prominent. Nuclear divisions were at first uniform but soon led to irregular nuclear divisions. Although the giant cell characteristically was thin-walled, it might form an irregularly thickened secondary wall with simple pits and without lignification,