Two studies were conducted to determine the infectivity of the lungworm, (Dictyocaulus viviparus) of cattle origin, in Rocky Mountain elk (Cervus elaphus nelsoni) or wapiti. In the first study, each of three 9-mo-old elk was administered 3,000 D. viviparus larvae from cattle using a nasogastric tube. In the second study, four 16-mo-old elk were each inoculated with 2,000 D. viviparus from cattle using a nasogastric tube. Elk were observed daily for signs of respiratory disease, and fecal samples were collected during the studies and evaluated for lungworm larvae using a modified Baermann technique. One elk was euthanatized during the patent period for recovery of adult lungworms, and three elk were euthanatized after larvae were no longer detected in feces. Lungworm larvae were not detected before inoculation in any of the 16-mo-old elk, but were detected 22 days after inoculation in one elk, 23 days after inoculation in two elk and 24 days after inoculation in all four elk. The prepatent period of this cattle isolate of D. viviparus in elk is therefore 22 to 24 days. The precise prepatent period was not determined in the three 9-mo-old elk, but larvae were detected in all three elk 25 days after inoculation. Numbers of larvae ranged from 1/to 101/g feces with peak larval detection occurring 32 to 50 days after inoculation. Elk shed larvae from 22 to 83 days after inoculation, and patent periods of the parasite ranged from 24 to 62 days. Clinical signs of respiratory disease, with the exception of mild coughing after exercise, were not observed during the infections. Results from this experiment indicated that D. viviparus larvae of cattle origin can mature in elk and larvae can be passed in large numbers in feces, but this cattle isolate of D. viviparus was not highly pathogenic in elk.