Nematode parasite infections are now being recognised as possibly the greatest disease problem of grazing livestock industries, worldwide. Often parasites were considered to be of greatest concern in countries of the tropics and subtropics. This is based on the perception that parasites are either not as pathogenic, or are better controlled, in grazing livestock industries in the temperate regions of the world. Unfortunately this is not the case. The hidden costs of nematode parasite infection, particularly in young ruminants, are substantial even in Europe. This is now especially so, when one considers that maintaining livestock for longer periods on pasture is becoming and economic, environmental and animal welfare necessity.