The type and the level of invasion by the endohelminths from nematodes and trematodes species were measured in naturally infected sheep by counting the number of eggs in faeces (FEC). The samples of faeces were taken before the spring grazing from randomly selected experimental group of sheep 7 days prior to (Day-7) and on the day of medication (Day 0, n = 15). Closantel (10 mg kg-1 body mass) and mebendazole (15 mg kg-1 body mass) were applied orally. On the 7th and 21st day after the treatment the value FECp was verified in the same group of animals and the degree of reduction with respect to the basal value FECb on the Day-7 and Day 0 (FECRT; 100x (1-(FECp/FECb)) was calculated. All species of endohelminths (Ostertagia, Trichostrongylus, Nematodirus, Strongyloides, Toxocara, Moniezia, Chabertia and Trichuris) found reacted to application of the drug by intensive reduction of the count of eggs excreted, in the range from 94% to 100%.