The morphology and enzyme forms of malaria parasites isolated from 50 wild caught specimens of Thamnomys rutilans from the Central African Republic have been studied and three distinct species of Plasmodium identified. One species has been confirmed as Plasmodium yoelii yoelii. Morphological features of both the remaining species correspond to those given by Landau (1965) in her original description of Plasmodium chabaudi. For one of these species the name P. chabaudi has been retained; the other species, which closely resembles subspecies of Plasmodium vinckei from other regions of Africa, has been designated Plasmodium vinckei petteri subsp. nov. P. chabaudi and P.v. petteri are distinguished from each other both in their morphology in the blood and sporogonic stages, and in their enzyme forms.