Infections of the common limpet, Patella vulgata were investigated along the coast of the Ards Peninsula, Co. Down. Samples were taken from around Portavogie, a small fishing port where seabirds aggregate to feed on fish offal, and from 14 sites along a 15 km transect. A new method of removing larval digeneans from the visceral hump of snails is described. The bulk of the parasite material was rediae of Cercaria patellae. The stage of development of these rediae varied significantly between hosts. Prevalence of infection was substantially greater close to Portavogie. The volume of parasite material recovered was greater for limpets close to rock pools than for those on rocks free from surface water at low tide. Among the latter limpets, the volume of parasite material in the visceral hump increased with increasing height on the shore. The greater part of the variation in parasite volume recovered from snails was determined by the size of the snail. The presence of larval digeneans was associated with progressive deterioration of host gonadal tissue and discolouration of the foot, mantle and digestive gland.