AbstractOn the basis of investigations on the cereal cyst nematode's distribution, it is presumed that one third of all the cereal growing areas in Denmark is infested to a degree, and that yield losses of 5 % or more may be assumed. This means an annual loss of about 100 million D.Kr. By using resistant cultivars every second year, the population ofHeterodera avenaeWoll. can be kept at a harmless level. It may be assumed that intensive growing of nematode‐resistant cereals includes a risk of promoting the occurrence of pathotypes other than the 2 known to exist in Denmark. So far, there is no indication for their existenc