In our effort to develop novel plant-derived acaricides, we examined the contact and fumigant toxicity of Asarum heterotropoides (Asarum sieboldii Miquel) essential oil constituents to the house dust mite Dermatophagoides farinae (Acari: Pyroglyphidae). Ten constituents, including methyl eugenol (relative amount 42.18 %), were identified by gas chromatography-mass spectroscopy (GC-MS) in the A. sieboldii Miq. essential oil. In contact toxicity tests, methyl eugenol (4.2 μg/cm(2), 24 h LD50) was most toxic to D. farinae, followed by benzyl benzoate (9.1 μg/cm(2)), A. sieboldii Miq. essential oil (37.7 μg/cm(2)), and dibutyl phthalate (DBP 57.9 μg/cm(2)). The potency of methyl eugenol and A. sieboldii Miq. essential oil was higher than benzyl benzoate and DBP, with mortalities of 100, 100, 94.6, and 13.2 %, respectively, after 2.5 h of exposure. In the vapor phase mortality bioassay, methyl eugenol and A. sieboldii Miq. essential oil resulted in 100 % mortality in closed containers after 24-h exposure, but only 4.7 and 7.9 %, respectively, in open containers, indicating that the toxicity in these tests was largely due to the vapor phase. Methyl eugenol and A. sieboldii Miq. essential oil merit further study as potential D. farinae control compounds.