This invention provides for dimericl-arylpyrazole compounds, of formulas (I), (II), and or salts thereof, and the use of these compounds against ectoparasites such as insects, arthropods and acarina. The resulting compounds may be used in veterinary formulations such as, for example, spot-on and pour-on formulations, which may be used for treatment, controlling and preventing of parasitic infections in warm-blooded animals and birds.
