Emerging rodenticide resistance to anticoagulants among Norway rats will have significant implications for rodent control.In this study we examined tissue samples from tails,and droppings of Norway rats in the Netherlands using a newly developed TaqMan PCR test for genotypic variation at codon 139 of the Vkorc1 gene,which is associated with anticoagulant resistance.In 34/61 rat tails (56%) ,a genotype was found that is directly linked to anticoagulant rodenticide resistance.In rat droppings,42/169 samples (25%) showed a resistance-mediating genotype.In some parts of the Netherlands,only resistance-mediating genotypes were found,which corresponds with the previous reports of licensed pest controllers of poor field efficacy of anticoagulants in some regions.In conclusion,multiple genetic mutations at codon 139 of the Vkorc1 gene were demonstrated in the country.As rodenticides are often considered as a final expedient during rodent control,their future efficacy should be closely monitored.