The transmission of Hammondia heydorni among sheep, goats, cattle, dogs and coyotes is described. Oocysts of H. heydorni, obtained from dog faeces by feeding naturally infected goat meat, were fed to an experimental goat. After 312 days tissues from this animal were fed to 2 dogs. One dog, which received goat muscle, shed oocysts, whereas the other dog which received brain, spleen, kidneys, lungs and liver did not. Oocysts from the dog fed goat muscle were fed to an experimental sheep. After 73 days sheep tissues were fed to a dog and a coyote, both of which shed oocysts 5–8 days later. A second isolate of H. heydorni was obtained by feeding naturally infected beef to a coyote. These oocysts were fed to a single goat and sheep and after 71 days, muscle from these 2 animals was fed to 2 dogs and 2 coyotes, all of which shed oocysts 5–8 days later. None of the animals inoculated with H. heydorni became ill and no Hammondia-like organisms were found in tissue sections from the herbivores. Another dog shed H. heydorni-like occysts between 7 and 10 days after ingesting naturally infected muscles from a moose. These results indicate that H. heydorni infects goats, sheep, moose and coyotes in addition to cattle and dogs.