In 1939 the sugar-beet nematode, Heterodera schachtii Schmidt, 1871, was found attacking the roots of sugar beets in the Blackwell district near Sarnia, Ontario. Studies were started in 1947 on the control and biology of this cyst-forming nematode, including the susceptibilities of various cultivated and weed plants to the nematode. Susceptibility was based on the presence or absence or degree of infestation of gravid white females on the roots.