Resistance against anthelmintics (worm-specific drugs) is well established problem among parasitic worms of livestock but is also an emerging problem in human medicine. The large intestinal roundworms (Ascaridida) such as equine parasite Parascaris univalens, porcine parasite Ascaris suum, poultry roundworm Ascaridia galli and human parasite Ascaris lumbricoides is of concern for animal and human health. Multiresistance is now being reported in Sweden and in the U.S. for the equine roundworm. In addition, treatment failures, is now a fact for A. lumbricoides in schoolchildren in Rwanda. Little is known about molecular mechanisms linked to AR. Currently no in vitro model is available for pathogenic roundworms. The aim of this project is to understand the molecular mechanisms of AR by developing an in vitro transgenic lines of the free-living nematode Caenorhabditis elegans, using the equine roundworm, P. univalens, as a model worm of Ascaridida. Selected candidates genes from P. univalens is expressed in C. elegans. The transgenic C. elegans are exposed to increasing concentration of anthelmintic drugs and the function of candidate genes is studied in response to drug treatment. Successful expression of candidate genes from P. univalens would enable us to interrogate the function of AR and to find biomarkers for sustainable control programs for monitoring resistance. Our hope is that the knowledge from this project about AR in P. univalens also can be used in other roundworms worms such as the pig, the chicken and the human.