In 3 separate studies, oxibendazole in drench and premix formulation was shown efficacious against larvae and adults of the genera Haemonchus, Ostertagia, Trichostrongylus, Strongyloides, Nematodirus, Cooperia, Bunostomum, Capillaria, Oesophagostomum, and Trichuris. In the first study, artificially infected calves were cleared of virtually all histotrophic larvae and adult parasites after medication with oxibendazole drench at a dose level of 10 mg/kg of body weight. Smaller doses (7.5 and 5.0 mg/kg) expelled 84 to 100% of the parasites. Oxibendazole at a dose level of 15 mg/kg in premix form was given to artificially infected calves 3, 7, or 42 days after infection in a 2nd study. Third stage and 4th stage Cooperia oncophora larvae were, respectively, 92 and 98% susceptible to the drug at day 3 and day 7 after infection; neither larval stages of Ostertagia ostertagi and of Oesophagostomum radiatum were susceptible. Premix given on day 42 after infection removed 83 to 100% of adult O ostertagi, Nematodirus spp, C oncophora, O radiatum, and Trichuris spp. In a 3rd study, calves harboring a mixture of parasitic stages from artificial and pasture-acquired infections were medicated with oxibendazole at a dose of 15 mg/kg in premix form. The burdens of larvae from the abomasum and small intestines were reduced 93 to 95%, respectively; the burdens of adults of 11 species of worms were reduced 87 to 100%.