Effects of the antiparasitic drug eprinomectin were studied in the laboratory and field experiments in Hokkaido, Japan, by pour-on administrations (500 lg/kg) on the pest fly Haematobia irritans (Linnaeus), nontarget coprophagous fly Neomyia cornicina (Fabricius), and the dung beetles Caccobius jessoensis Harold and Liatongus minutus (Motschulsky). Eprinomectin excreted into cattle dung was highest at 3 days post-treatment in both experiments, then it declined rapidly at 7 days and was not detected on or after day 14 post-treatment. In laboratory experiments, pupation and emergence rates of H. irritans and N. cornicina were hampered from 1 to 14 days posttreatment. There were no significant differences in the numbers of brood balls constructed by C. jessoensis in dung from treated and control cattle. Adult emergence rates of C. jessoensis were significantly reduced on days 1 and 3 post-treatment in dung from treated cattle. There were no significant differences in the numbers of brood balls constructed by L. minutus in dung from treated and control cattle, but survival rates of larvae were significantly reduced on days 1 and 3 post-treatment. In field experiments, the numbers of brood balls by L. minutus recovered from beneath dung pats were significantly larger in number in dung from treated cattle, suggesting that adult beetles are attracted to dung pats from treated cattle. Survival rates of larvae in these brood balls of L. minutus were significantly reduced 1 day post-treatment in dung pats from treated cattle, and equivalent levels to the control were restored 7 days post-treatment. The results are discussed in relation to the effects of endectocides on nontarget insects in grazing pastures.