Dictyocaulus viviparus infections in Rocky Mountain elk (Cervus canadensis of Teton County were surveyed by fecal analyses during spring, summer and winter and by fecal analyses and necropsies during fall hunting seasons, 1968–1973. Prevalence of the lungworms was relatively high: 32–70% during the spring; slightly lower, 30–47%, during the summer; 21–39% in the fall; and declined to the annual low of 8–19% during the winter. Conversely, elk summering on Big Game Ridge showed an increase in prevalence of D. viviparus from 1969 to 1973. Decreases in prevalence of lungworms were noted on the National Elk Refuge at Jackson after management changes were effected in 1971.