In studies using three sibling F-1 clones from each of five crosses between Solanum tuberosum and different wild tuber-bearing Solanum species, root leachate hatching activity towards each of the two potato cyst nematode (PCN) species, Globodera rostochiensis and G. pallida. segregated independently. Sephadex G-10 fractionation of the leachates of S. sucrense-hybrid clones revealed differences between clones in the hatching factor elution profiles for the two PCN species. Analysis of individual hatching factors indicated examples: both of selectivity (both PCN species hatched in response to a particular hatching factor, but at different levels of hatching response) and of specificity (only one PCM species hatched in response to a particular hatching factor) of hatching factors. The hatching factor profiles of the S. sucrense-hybrids indicated segregation of hatching factors from the parents, but also detected novel factors unique to specific hybrid clones. Total hatching activity of the root leachate of the S. sucrense clones was positively correlated with the proportion of S. tuberosum-derived hatching factors.