Abstract. We studied the antigens of adults and third-stage larvae of the meningeal worm, Parelaphostrongylus tenuis, in an attempt to identify potential serodiagnostic molecules for this important infection of wild ungulates. Soluble extracts of P. tenuis adult worms and third-stage larvae were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional (2D) electrophoresis and analyzed by immunoblotting using purified rabbit anti-P. tenuis immunoglobulin G (IgG). The IgG antibodies were obtained from animals immunized with P. tenuis adult worm or third-stage larva soluble extract and serum from elk infected with P. tenuis. Out of more than 75 antigens (as shown by 2D electrophoresis and immunoblotting), 7 antigens from adults (four 170-120-kD molecules with isoelectric points between 6.0 and 6.6, two 55kD molecules with isoelectric points of 5.6 and 5.8, and one 13-kD molecule) and 2 antigens from thirdstage larvae (one 25-30-kD molecule with an isoelectric point of 6.3 and one 13-kD molecule) distinguished P. tenuis from two other nematodes, Dictyocaulus viviparus and Trichinella spiralis. Initial results using serum from experimentally infected elk indicate that this serum recognized a similar profile of P. tenuis antigens when compared with the serum from immunized rabbits. This research has set the foundation for the development of a test for P. tenuis infections in wild and recently domesticated elk and other ungulates.