The effects of lanthanum chloride and ruthenium red on hatching of Globodera rostochiensis do not show that free calcium ions are essential for the initiation of hatching. Lanthanum chloride is not an effective inhibitor of hatching but is a moderately effective hatching agent. It partially inhibits the hatch-stimulating activity of potato-root exudate, possibly by complex formation. Ruthenium red effectively inhibits exudate-initiated hatching by inactivating the hatching factor and inhibiting nematode movement.