It is the general opinion that the haemoproteid blood parasites of chelonians belong to the genus Haemoproteus. Different specific names have long been assigned to this parasite in birds, but some past authorities have accepted only a single species, H. metchnikovi, for all those haemoproteids recorded in a wide range of chelonian genera throughout the world. In the present study, a comparison of one such organism in the tortoise Geochelone denticulata with another in the river turtle Peltocephalus dumerilianus, from Amazonian Brazil, has revealed clear morphological differences. These distinguish the parasites from each other, H. metchnikovi and the other named species of chelonian Haemoproteus for which adequate descriptions are available. We have assigned to them the names Haemoproteus geochelonis n.sp. and Haemoproteus peltocephali n.sp.