Comparison of potato root leachates (PRL) collected from the roots of mycorrhizal (using the mixed-isolate inoculum, Vaminoc) and non-mycorrhizal potato cv. Golden Wonder confirmed that mycorrhization caused a significant increase in hatching activity towards Globodera pallida but not G. rostochiensis. After fractionating the leachates by low pressure molecular exclusion/anion exchange liquid chromatography, several potato cyst nematode (PCN) species-specific hatching factors (HF) were found only in PRL from mycorrhizal plants. Leachate from mycorrhizal plants also contained more of several of those HF common to PRL from both mycorrhizal and non-mycorrhizal plants. Significantly more hatching factor stimulants (HS) active towards both PCN species were found in the PRL from mycorrhizal than from non-mycorrhizal plants; several HS were specific to mycorrhizal plants. No differences (quantitative or qualitative) were observed in hatching inhibitor (HI) levels between PRL from mycorrhizal and non-mycorrhizal plants. Mycorrhization of potato plants resulted in a 20% increase in carbon but a 48% decrease in nitrogen concentrations of the PRL compared to that from the non-mycorrhizal plants.