While-tailed deer (Odocoileus virginianus) were successfully infected with Haemonchus contortus of sheep origin. Individual deer in each of three groups were inoculated with 0. 25,000, and 100,000 larvae respectively. Severity of infection was related to dose and signs of infection were most obvious in the heavily inoculated animals. Infected deer were weak, emaciated, and anemic, similar to the clinical response in sheep. Hemoglobin, packed cell volume, and total serum protein values for both infected groups were significantly lower than for the controls. Inhibition of larval growth was noted in both infected groups, but was most pronounced in the group which received 100,000 larvae. Inhibition of egg production was also noted in this group. The potential importance of H. cortortus in deer populations was discussed.