Between 1986 and 1995, 548 fecal samples were collected from 41 species of bats (Molossidae, Mormoopidae, Phyllostomidae, Thyropteridae, and Vespertilionidae) from New Mexico, California, Baja California Sur (Mexico), and Bolivia. Of these, the feces of 28 (5%) bats, including Antrozous pallidus, Myotis ciliolabrum, Myotis lucifugus, and Myotis yumanensis (Vespertilionidae), contained oocysts representing at least 3 species of Eimeria. A new species of eimerian from M. lucifugus (3/27, 11%) and M. yumanensis (8/70, 11%) is described. Sporulated oocysts are ellipsoidal, 22.3 x 14.8 (18-25 x 13-16) mu m with micropyle (similar to 2 mu m) and polar granules (1-4), but an oocyst residuum is absent. The oocyst wall is slightly rough exteriorly and has 2 layers (total less than or equal to 1 mu m thick). Football-shaped sporocysts are 8.1 x 6.6 (8-11 x 5-7) mu m, each with a Stieda body and granular sporocyst residuum present. A new eimerian from M. yumanensis (4/70, 6%) and M. ciliolabrum (1/12, 8%) also is described. Sporulated oocysts are spheroidal to subspheroidal, 15.0 x 14.1 (14-16 x 14-16) mu m, with micropyle and oocyst residuum absent; a polar granule is present. The wall is smooth and has 2 layers (total <1 mu m thick). Sporocysts are football shaped, 7.1 x 5.9 (6-9 x 5-7) mu m, each with a Stieda body and sporocyst residuum. The sporulated oocysts of a third morphotype, found in A. pallidus (12/85, 14%), were indistinguishable from those of Eimeria arizonensis, a species typically found in murid rodents. The currently recognized species of bat Eimeria are listed, and a dichotomous key is provided.