The effects of cyst components of the potato cyst nematode, Globodera rostochiensis, on in vitro hatching of juveniles were evaluated. Aqueous homogenates of eggs and cyst walls, and aqueous rinses of cyst walls and eggs were examined. Homogenates of cyst walls or rinsates of either cyst walls or eggs each significantly increased hatch of juveniles five-fold compared with sterile distilled water controls. Cyst or egg homogenates induced significant increases (7.7-9.0-fold) in hatch of juveniles compared with controls. These values represent approximately 24.8-29.0% of the 31-fold induction of hatch of juveniles by potato root diffusate, routinely used to stimulate hatch in G. rostochiensis. The hatch inducing factor(s) in cyst homogenates was thermostable and retained activity after repeated freezing and thawing. Filter fractionation of cyst homogenate localised activity between molecular mass 0.5 kDa and 5 kDa, with no hatch inducing activity present above 5 kDa. Apparent depression of hatch induction at high concentrations of non-fractionated cyst homogenates suggests the presence of hatch inhibitors.