The lone star tick, Amblyomma americanum Linnaeus, is ubiquitously present in the southeastern United States and will readily parasitize humans and companion animals. Fipronil is the active ingredient in several topically applied products used to manage ticks and fleas on companion animals. Reducing ectoparasite infestations on companion animals decreases the risk that pathogens vectored by these pests are transmitted to these animals and their owners. However, dependence on acaricides can promote the development of resistance. In this study, the Food and Agriculture Organization of the United Nations larval packet test was used to determine the lethal concentration (LC) values and discriminating concentration (DC) for fipronil in the lone star tick. The DC was calculated as 0.02080%. The low magnitude of the DC value suggests that fipronil is an effective active ingredient for A. americanum management. With the LC and DC values determined, emergent resistance can be monitored, potentially allowing for intervention should tolerance develop in A. americanum populations that are in frequent contact with humans and their companion animals.