During cultivation of asparagus plants growth can be inhibited and yield can be reduced by plant-parasitic nematodes. Plant raising companies assume that the root lesion nematode (Pratylenchus penetrans) can cause severe yield loss in asparagus plants. However quantitative information about yield reduction in relation to the degree of infestation of this nematode species in the field is lacking. Research was done in The Netherlands by Applied Plant Research (part of Wageningen University and Research Centre) to determine the maximum degree of yield loss of asparagus plants at high infestation levels of P. penetrans and to establish the height of the tolerance limit for this nematode species. Also was investigated whether a field application of a granular nematicide could prevent or reduce yield loss caused by P. penetrans. Research was done in the field at sandy soils at the PPO location near Vredepeel in The Netherlands over a period of two years. In the first year the most suitable field was selected and on this field different infestation levels of P. penetrans were created. In the second year asparagus was cultivated and plant yield (number and quality of deliverable plants and financial yield) was calculated. At high infestation levels of Pratylenchus penetrans maximum yield loss was 12% (which can mean a financial loss of 7.000 C per ha). Yield started to decrease at very low infestation levels of P. penetrans and no statistical reliable tolerance limit could be calculated. Field application of 40 kg per ha of Vydate 10 G just before sowing of asparagus, could almost completely prevent yield loss caused by P. penetrans. After harvest infestation levels of P. penetrans were much lower than could be expected if asparagus was a non-host for this nematode species. In this paper therefore it is suggested that asparagus plants are (actively) controlling P. penetrans.