Hatching factors with activity towards Globodera rostochiensis were isolated from the root leachates produced by 1500 potato plants grown in gravel. In total, nine hatching factors, each with molecular weight 530.5 Da, were isolated. The main differences in the daughter ions produced from different hatching factors after fragmentation by mass spectrometry occurred between 245 and 500 Da. The main hatching factor, HF E, was found in extremely low concentrations in the leachate (less than 2.9 x 10(-5) % of recovered organic material) and was active in vitro at less than 2.1 x 10(-8) M. Separation of the different hatching factors during purification was found to decrease the percentage hatch achieved in vitro at optimum concentration.