This symposium volume considers some of the recent developments in veterinary parasitology. The significance of epidemiology is illustrated by a paper on the lung worm Dictyocaulus viviparus. The current position of vaccine application and development is discussed in relation to both Dictyocaulus and gastrointestinal nematodes. Immunological responses of sheep to infection with Haemonchus contortus are reviewed and of cattle to infections with gastrointestinal nematodes. Drug resistance in veterinary parasites is discussed in general terms and considered from an electrophysiological perspective. The possibility of controlling nematode infections by using predacious micro fungi is examined while current methods for diagnosis of gastrointestinal nematodes are also evaluated. The impact of nutrition in pathogenesis of bovine trypanosomiasis is reviewed and the status of the cattle nematode Onchocerca ochengi as a model for studies on human onchocerciasis is discussed.