SummaryOne of the alternative methods of parasite control, of particular importance in sustainable farming, is the use of medicinal plants. The specifi c aim of the present fi eld trial was to assess the anti-parasitic effects of herbal extracts contained in a commercially available lick formulation for sheep. At the outset of this study conducted during the grazing season, all animals were de-wormed and then randomly assigned to one of the two separately kept groups (treatment and control), each consisting of 25 animals (11 ewes and 14 lambs). The treatment group received mineral licks containing the extracts of the plants with anti-parasitic properties, while control animals received standard mineral licks ad libitum. Rectal fecal samples were collected monthly from all animals for the McMaster analyses. There were no signifi cant differences in the prevalence and intensity of helminth infections between the treatment and control groups. Thus, we were not able to ascertain the effi cacy of the commercial herbal de-wormer tested for the control of gastrointestinal helminths in grazing ewes and their lambs.