This invention provides for dimeric1-arylpyrazole compounds, of formulas (I), (II), and (III): 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.
