Genomic DNA isolated from the four Dictyocaulus species D. viviparus, D. eckerti, D. filaria and D. arnfieldi was compared by random amplified polymorphic DNA polymerase chain reaction (RAPD)-PCR to get additional information whether lungworms from fallow deer belong to a separate species (D. eckerti) or have to be regarded as an isolate of D. viviparus in wild ruminants. The resulting banding patterns of the electrophoresed PCR products were compared to assess the degree of genetic differences between the different lungworms. For the two D. viviparus isolates a similarity coefficient of 93.4% was calculated, whereas the similarity coefficient of D. viviparus, D. eckerti, D. filaria and D. arnfieldi ranged from 12% to 32%. The similarity coefficient of 32% between D. eckerti and D. viviparus compared with the intraspecies similarity of 93.4% indicates that D. eckerti most likely belongs to a separate species and is not a D. viviparus isolate of wild ruminants.