Presence of 2,4-dichlorophenol (2,4-DCP) in extracts of fed and nonfed adult female Dermacentor variabilis (Say) by gas chromatography and mass spectroscopy (GC/MS) is reported. 2,4-DCP was detected as part of a mixture with 2,6-dichlorophenol, which is the attractant sex pheromone in this species in a 1:9 ratio, respectively. Extracts did not contain the monochlorinated phenols, 2-chlorophenol and 4-chlorophenol. None of these chlorophenols were detected in eggs. 2,4-DCP is comparable in efficacy to 2,6-DCP as an attractant sex pheromone, prompting attraction, arrestment and feeding posture behavior by fed males. It is also present in the female adult.