Cryptosporidium meleagridis, a protozoon first observed in turkeys, has been linked by several investigators to cryptosporidiosis in humans. C. meleagridis is the only known Cryptosporidium species that infects both avian and mammalian species. We describe the successful propagation of C. meleagridis (isolate TU1867), originally purified from a patient with diarrhea, in laboratory animals including chickens, mice, piglets, and calves. TU1867 was readily transmitted from one animal host to another, maintaining genetic homogeneity and stability. The rate of infectivity and virulence of TU1867 for the mammalian species were similar to those of Cryptosporidium parvum. Laboratory propagation of genetically and phenotypically stable and well-characterized reference isolates, representing various Cryptosporidium species, particularly those infectious to humans, will improve considerably the spectrum and quality of laboratory and field investigations on this medically important protozoa.