The persistent anthelmintic effect of ivermectin as a topical treatment at 500 µg/kg was evaluated against induced infections ofOstertagia ostertagi, Trichostrongylus axeiandDictyocaulus vivparusin calves. The results showed a highly significant (P<0.001) anthelmintic activity for at least 14 days againstO. oslertagiandT: axei(>99 per cent efftcacies) and for at least 28 days (98 per cent efficacy) againstD. viviparus.