Use of the enzyme-linked immunosorbent assay (ELISA) to detect anticoagulant compounds in non-target animals (companion animals, livestock, and wildlife) is described. Such immunoassays are sensitive to the presence of anticoagulants in the ng/mL range, which is parts per billion (ppb) of biological material. This assay strategy is explained, as is progress to date in detecting diphacinone and chlorophacinone.