Introduction: Most grazing ruminants are infected by a variety of helminth parasites that have a massive impact on their health, welfare and their production. In that context, diseases caused by gastrointestinal nematode parasites are important animal health issue. The main mean to control such parasites relies on the use of anthelmintic drugs. However, intensive use of chemicals has selected drug-resistant parasite populations in many animal species. This includes resistance to the latest developed broad-spectrum macrocyclic lactones (MLs) such as ivermectin (IVM). There is now considerable evidence that ML resistance is a polygenic trait in nematodes, but the molecular mechanism(s) of ML resistance remains to be resolved. The problem is worsened by the lack of efficient tools to track resistance. Materials and Methods: In that context, we have developed a stable fluorescent probe of IVM, IVM-FLUO, and were able to visualize and quantify IVM into Caenorhabditis elegans using confocal imaging. We have compared the distribution and signal intensity of IVM-FLUO in susceptible and ML-resistant strains. For the first time, we could visualize and map the parental IVM in the whole worm. Results: Signal quantification revealed a higher IVM amount in wild-type animals compared to the IVM-resistant worms, in line with a link between IVM concentration in the worm and IVM resistance status. Discussion: Knowledge on IVM distribution in nematodes is actually a very important missing aspect. Better understanding IVM resistance will allow us to propose specific treatment/combinations to improve its efficiency. IVM-FLUO is an innovative tool that meets the expectations of clinicians and breeders concerned about the loss of drug efficacy. Its development will allow the evaluation of the efficacy of anthelmintic drugs and the resistance status of pathogenic parasites in livestock. In addition, it represents a valuable asset for the research of drug resistance mechanisms in general