A species of syngamid nematode belonging to the genus Syngamus was found in the respiratory tract (terminal trachea to bronchi) of tundra voles (Microtus oeconomus) collected on St. Lawrence Island, Alaska (USA). Its prevalence in June 1989 was >29% (12 of 41 male voles and seven of 24 females) in the village of Savoonga, while no nematodes were found from 41 voles collected in the village of Gambell. Lesions included dilatation of parasitized respiratory ducts and peribronchial and perivascular cuffing by lymphoid cells, mainly plasma cells, in parasitized lobes. Morphologically, this syngamid species differed from S. microtinae reported previously from the same host species as well as from other syngamids known from avian hosts.