In a flock of 20 ewes naturally infected with those parasites of sheep most common in Greece, and kept indoors during the whole trial, oxfendazole at the dose rate of approximately 2–9 and 2–8 mg/kg body-weight was tested as a 4 g bolus containing 112 mg active ingredient and a 2–265% suspension. The evaluation of its efficacy was based on the necropsy findings which were also supported by faecal egg counts. No differences in efficacy were noticed between the two formulations of the drug. Both bolus and suspension proved to be 100% effective against Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus axei, T. colubriformis and Chabertia ovina. The efficacy against Cooperia oncophora, Nematodirus spathiger, Bunostomum trigonocephalum, Oesophagostomum columbianum and Moniezia expansa could not be evaluated, because these species, though not found in any of the treated animals, were found in fewer than three controls.