Emerald ash borer (Agrilus planipennis Fairmaire), an Asian species discovered in June 2002, is established in much of southeastern Michigan and Windsor, Ontario. Larval feeding under the bark disrupts vascular tissue, eventually girdling and killing ash trees (Fraxinus sp.). More than seven million green ash (F. pennsylvanica), white ash (F. americana), black ash (F. nigra) and blue ash (F. quadrangulata) trees in southeastern Michigan are dead or dying. In its native range, A. planipennis reportedly attacks other genera including Ulmus sp., Juglans sp., and Pterocarya sp. Attacks on these genera have not been observed in North America, but there is much concern about potential host switching as ash trees die. Members of these genera and species closely related to Fraxinus, including American elm (U. americana), black walnut (J. nigra), hickory (Carya sp.), privet (Ligustrum sp.), and lilac (Syringa sp.) are common in landscapes and wooded areas in North America. To evaluate A. planipennis host range, we quantified oviposition and larval development on ash and non-ash species in no-choice and two-choice laboratory bioassays and on bolts of ash and non-ash species attached to infested trees in the field. Preliminary results suggest that A. planipennis will oviposit on species other than ash. Early instar feeding is limited and development will be compared on logs from the lab and field studies in late summer to determine whether other species are at risk.