During 3 collecting expeditions between October 1996 and December 1996, fecal samples were obtained from 43 adult Gonocephalus grandis from Tanah Rata and the Cameron Highlands in Peninsular Malaysia. Two species of coccidia (Isospora gonocephali n. sp. [9/43, 23%] and Eimeria cameronensis n. sp. [3/43, 7%]) were discovered. Sporulated oocysts of I. gonocephali are subspherical to ovoidal, 22.3 x 18.7 (19-25 x 17-23) microm with a bilayered wall composed of a thin inner wall and a striated outer wall with a pitted surface; oocyst residuum absent; 1 polar granule present; sporocysts are almond-shaped, 13.5 x 9.2 (12-15 x 8.5-10) microm, Stieda body broad, domelike, substieda body fanlike, sporocyst residuum consisting of coarse, nonuniform granules in an amorphous cluster; sporozoites sausage-shaped with 1 large terminal, refractile body and lay randomly in the sporocyst. Sporulated oocysts of E. cameronensis are bilayered, smooth-walled, ellipsoidal, 26.5 x 12.4 (25-28 x 12-13) microm; with 1, small, polar granule composed of 2-3 splinter-like structures fused together; oocyst residuum absent; sporocysts ovoidal, almost rectangular-shaped 8.8 x 6.6 (8-9 x 5-7) microm, with no Stieda or substieda bodies, containing scattered residuum and 2 sausage-shaped sporozoites with 1 terminal, ovoidal refractile body. No individual lizard was host to both coccidian species.