Nine Trichomonas-free band-tailed pigeons (Columba fasciata fasciata) trapped in Colorado died from experimental infection with Jones' Barn Trichomonas gallinae 7.1 days (av.) post-inoculation. Three experimentally infected domestic pigeons (C. livia) used as controls died 5.7 days (av.) post-inoculation. Three band-tailed pigeons from Colorado naturally infected with avirulent T. gallinae did not produce sufficient antibody to protect them from virulent T. gallinae. Trichomonads obtained from a fatal case of trichomoniasis in a band-tailed pigeon from California killed a band-tailed pigeon from Colorado; they did not kill five domestic pigeons but did induce severe oral caseation.