Young peafowl (Pavo cristatits), when tested for susceptibility to histomoni-asis by feeding embryonated eggs of Heterakis gallinarum carrying Histomonas meleagridis, were almost as susceptible to the disease as young Beltsville Small White turkeys. The disease developed more slowly, but, by 14 days after inoculation morbidity was 100% and 84% died. The young peafowl is so much more susceptible to histomoniasis than either chickens or pheasants that it should never be permitted to mingle with these birds, except where earthworms, the means of transmission of Heterakis, are absent. However, the young peafowl is unimportant in transmitting Histomonas meleagridis because the cecal worm rarely completes its life cycle in a young bird of this species when histomoniasis is present.