Eprinomectin is a new endectocide of the avermectin chemical group developed for use in cattle. To establish its effectiveness against Cooperia spp., Dictyocaulus viviparus, Haemonchus contortus, Nematodirus helvetianus, Oesophagostomum radiatum, Ostertagia ostertagi, Trichostrongylus axei and Trichostrongylus colubriformis (immature infections only), six trials were conducted in Europe at two trial sites. In each trial, animals were artificially infected with a number of nematode species and treated with eprinomectin. In three trials, the nematodes were expected to be at the fourth larval stage of development at the time of treatment, and at the adult stage at the time of treatment in the other three trials. When compared with the untreated control groups, efficacy against the adult and immature nematode infections was > 99% for all the nematode species examined. There was no difference in efficacy between groups of animals with clipped hair at the application site, and those with long hair. Subsequent examination of the application sites, both visual and by palpation, showed no gross reactions to the applied treatments.