A mild form of type II ostertagiosis was recorded in a group of 12, 22-month-old red deer stags, slaughtered in an abattoir in April 1989. The animals appeared clinically normal but they were light and in rather poor condition. Mixed ostertagid infections were present in very variable numbers. In the seven most heavily infected animals, 70 per cent of the worms were in the early fourth stage and assumed to be hypobiotic. In some animals the worms were maturing and in these there were lesions similar to those associated with bovine ostertagiosis.