counts are of little value in diagnosis which is best made on grazing history, clinical signs, and is possible, a post-mortem examination. DIAGNOSIS Several drugs are highly effective against Nematodirus infections especially levamisole, ivermectin or one of the modern benzimidazoles, fenbendazole, oxfendazole or albendazole. The response to treatment is usually rapid and if diarrhoea persists coccidiosis should be considered as a complicating factor. TREATMENT With the exception of N. battus, which requires special consideration, disease due to monospecific Nematodirus infections is rarely seen. Instead, they are usually part of the worm burden of trichostrongyloid species which are responsible for the syndrome of parasitic gastroenteritis in sheep and as such may be controlled by the measures outlined below. CONTROL Since N. battus infection of lambs has a unique epidemiology, its control is best considered separately. Due to the annual hatching of N. battus eggs in spring, the disease can be controlled by avoiding the grazing of successive lamb crops on the same pasture. Where such alternative grazing is not available each year, control can be achieved by anthelmintic prophylaxis,