A new species of Isospora is described from the fecal contents of the white-chinned woodcreeper, Dendrocincla merula merula from Guyana and Dendrocincla merula barletti from Peru. Sporulated oocysts are subspherical to ovoid, 19.2 × 16.5 (15–23 × 14.5–19) μm, with a smooth, colorless, bilayered wall. The average shape index is 1.2. No micropyle or oocyst residuum are present, but the oocysts contain one polar granule. Sporocysts are ovoid, 12.9 × 8.3 (12–14 × 7–10) μm, average shape index of 1.7 with a smooth, single layered wall and composed of a small, knoblike Stieda body and a slightly larger, bubble shaped substieda body. The two sporocysts each contain a compact residuum composed of coarse, non-uniform granules and four randomly arranged, vermiform sporozoites each with a terminal refractile body and a centrally located nucleus. DNA sequences representing ITS-1 and ITS-4 regions of the 5.8S rDNA gene from the two isolates were amplified and compared. In addition to the two isolates showing similar morphological characteristics, they also had identical nucleotide sequences for the ITS-1 and ITS-4 regions of the 5.8S ribosomal gene.