It now appears that Plasmodium cynomolgi, Plasmodium knowlesi, Plasmodium inui, and Plasmodium schwetzi are true zoonoses, although the latter, as Plasmodium ovale, may be an anthroponosis as well. Plasmodium malariae and Plasmodium rodhaini are generally accepted as being synonymous; if this is true, and it probably is, then this African quartan parasite is either one, i.e., a zoonosis or an anthroponosis, depending on which group of primates gave it origin. Certain African-Asian forms, Plasmodium gonderi for example, appear to be neither. The Central and South American primate malarias pose a different problem, for it is held that these malarias appeared only after 1492 when man, carrying P. malariae and Plasmodium vivax invaded this area from Europe. Consequently, each infection appeared in the monkeys as an anthroponosis. If this is true, synonymy is inevitable. If, on the other hand, Plasmodium brasilianum is a valid species, it acts as a zoonosis. There is reasonable doubt that Plasmodium simium acts in the same capacity.