Blood films and fecal samples of the lesser prairie-chicken (Tympanuchus pallidicinctus) were examined for parasites when we surveyed specimens captured during a radio-tracking study conducted in Chaves County, New Mexico (USA). All birds were captured on the Caprock Wildlife Habitat Management Area, administered by the Bureau of Land Management. Samples were collected in late March, April, and early May 1998-2000. Oocysts were detected in five of 64 (8%) birds sampled and, upon sporulation, were determined to be an Eimeria species. This is the first eimerian reported from the lesser prairie-chicken and is described here as a new species. Sporulated oocysts are ellipsoidal, 27.1 x 22.7 (22-32 x 18-26) microns, with micropyle absent, but oocyst residuum and polar granule present. Sporocysts are ovoidal, 11.9 x 7.8 (10-14 x 6-10); a Stieda body, and sporocyst residuum are present, as is a small, indistinct substieda body. Inspection of blood smears revealed four cases of Plasmodium infection of 32 (13%) individuals sampled. The characteristics of this plasmodiid are consistent with the description of Plasmodium (Giovannolaia) pedioecetii, previously found in T. pallidicinctus (Stabler, 1978).