In this paper the different options for the diagnosis of gastrointestinal nematode infections are discussed. Diagnostic tests
have a role in confirming the clinical diagnosis of parasitic gastroenteritis, but are more important for herd health
monitoring of nematode infections, in particular for cattle. Therefore, emphasis is placed on discussing the available
diagnostic parameters on their usefulness for that purpose. For clinical diagnosis the clinical signs, combined with the
history of the animals is usually sufficient and a laboratory confirmation is not required. Faecal egg counts are, with two
exceptions, not suitable for confirmation of the clinical diagnosis, because correlation between faecal egg counts and
infection levels is usually low. These exceptions are the diagnosis of haemonchosis in small ruminants and the detection
of anthelmintic resistance. This also limits the value of DNA-based tests of faecal material; even quantitative tests of
nematode species specific DNA will have little value for diagnosis and monitoring. Pasture larval counts and worm counts
are useful parameters for basic epidemiological studies on nematode infections. However, they are too laborious to be used
for either routine diagnosis or monitoring. Blood parameters, such as gastrin and pepsinogen and serology are valuable
tools for diagnosis. Pepsinogen and ELISAs based on recombinant proteins show most promise as parameters for herd
health monitoring. However, extensive epidemiological studies are still needed before these parameters can be implemented
in routine herd health monitoring schemes for parasitic gastroenteritis.