The alarming development of triple resistant Parascaris spp. is an increasing threat to foal health and the equine industry, due to the risk of increasing veterinary costs and loss of foals. A continued development of triple resistant roundworms in Sweden would be devastating for foals and breeders. It is therefore of uttermost importance to gain more knowledge about anthelmintic resistance and to develop tests to detect resistant parasites. The aims of this project are to 1) evaluate the spread of resistance to the substance fenbendazole (Axilur®) in foals in Sweden 2) identify markers for detection of resistance and development of a method for rapid detection of resistant parasites 3) develop an in vitro method for study of drug resistance and screening of new drug candidates. The results from this project will be used to monitor further development of resistance and be included in new sustainable parasitic control guidelines.