Specimens of Dictyocaulus spp. were extracted from the respiratory tracts of 3 ruminant hosts including roe deer (Capreolus capreolus), red deer (Cervus elaphus), and chamois (Rupicapra rupicapra) from wild populations in the province of Le6n, northwestern Spain. The near-complete nuclear small-subunit ribosomal RNA gene, and 2 regions of the large-subunit ribosomal RNA gene, were amplified by PCR and sequenced. The SSU rDNA gene sequences indicated a high level of similarity between the isolate from C elaphus and the published sequences for Dictyocaulus eckerti. SSU rDNA gene sequences were identical in the isolates from C. capreolus and R. rupicapra, and both corresponded to published sequences for D. capreolus. The LSU rDNA gene sequences differed in isolates from the latter 2 hosts, indicating the possible presence of an undescribed Dictyocaulus sp. in R. rupicapra. These results showed that the LSU rDNA gene sequences are useful indicators of genetic and species diversity in species of Dictyocaulus.