Ivermectin, one of the new avermectin group of anthelmintics, was more than 99 per cent effective in removing all stages of Ostertagia ostertagi including inhibited larvae, and adult Trichostrongylus axei when administered to cattle orally at 100 microgram/kg body-weight or subcutaneously at 100 and 200 microgram/kg body-weight. High efficacy (> 98.6 per cent) was also obtained against adults and inhibited larvae of Cooperia oncophora at 100 microgram/kg orally or 200 microgram/kg by subcutaneous injection. The latter treatment caused an 82.3 per cent reduction of adult Nematodirus helvetianus.