Determine the resistance of the tick Dermacentor nitens to metrifonate (Neguvon®, Bayer©, Germany), cypermethrin (Ganabaño®, Novartis©, USA), and amitraz (Triatox®, Schering Plough ©, USA). A non-probabilistic convenience experimental study, five plots where teleogines 120 engorged D. nitens were collected, the teleogines were subjected to immersion test according to Drummond. It was found that the treatment was less chemoresistance produced amitraz 97% effective, followed by 93% cypermethrin and 53% respectively metrifonate. An oviposition evaluation, it was found that amitraz is the most effective 23%, cypermethrin 18% and then metrifonate 1%. The percentage hatching assessment was higher for metrifonate 18.97%, cypermethrin 4.70% and Amitraz 1.68% respectively. It is concluded that amitraz is the most effective acaricide in vitro not only affect adults but to eliminate the cycle of D. nitens, but its use in practice is unlikely in vivo by toxic effects in horses. Among the products used in horses, cypermethrin is the drug of choice.