An in vitro immersion bioassay was used to compare the efficacy of selected pyrethroids against a deltamethrin-resistant strain of rabbit ear mite (Psoroptes cuniculi). A lack of cross-resistance between bromo (deltamethrin) and chloro analogues (cypermethrin) of ! -cyano-3-phenoxybenzyl - dihalovinyl-dimethylcyclopropane carboxylate was detected. Whereas deltamethrin proved to be inactive (48-h mortality 21.9% at 1000 mg/kg), each cypermethrin isomer mixture tested, including alpha-cypermethrin [1R(cis) ! S + 1S (cis) ! R] and theta-cypermethrin [1R(trans) ! S + 1 S (trans) ! R] and their mixture at a ratio of 4/6, beta-cypermethrin, showed high efficiency (48-h mortality S 95% at 1000 mg/kg).