Of 63 specimens of the lizard Mabuya mabouya (Scincidae) examined in Pará State, Brazil, 31 showed one or more haemosporidians in the peripheral blood. These included Garnia (Plasmodium) morula (Telford, 1970), Lainson, Landau & Shaw, 1971; Plasmodium tropiduri and P. diploglossi Aragão & Neiva, 1909; a Plasmodium species close to P. diminutivum Telford, 1973a; and a new species of Saurocytozoon Lainson & Shaw, 1969a. Eleven different combinations of these parasites were noted, emphasizing the care needed in avoiding erroneous descriptions based on mixed infections. This is especially so when G. morula is mixed with P. tropiduri or other species with small, rounded gametocytes occupying a polar position in the red blood cells. Of 18 skinks infected with G. morula, 10 had pure infections, as judged by repeated examinations over long periods. The morphology of the Brazilian parasite is very similar to that described for G. morula from Panama (Telford, 1970): no malarial pigment could be demonstrated in any stage of the infection, including ookinetes and possible early oocysts which were studied in experimentally infected Culex pipiens fatigans. Ookinetes and rounded forms, possibly representing uninucleate oocysts, persisted in these insects up to 24 h after the blood-meal, but developed no further. C. p. fatigans is thus unlikely to be a natural vector of G. morula. Saurocytozoon mabuyi sp.nov. is described in M. mabouya: the gametocytes develop in the lymphocytes and monocytes of the circulating blood and reach maximum size in 19–28 days. The parasite can be distinguished from the other known species, S. tupinambi of the teiid lizard Tupinambus nigropunctatus, by its smaller gametocytes. Nothing is known of the sporogonic cycle. Differences between the sporogonic stages of S. tupinambi and Leucocytozoon are listed.