Eimeria palustris sp. n. and Isospora hammondi sp. n. are described from the marsh rice rat, Oryzomys palustris, from Alabama. The ellipsoidal oocysts of E. palustris measure 19 to 28 by 16 to 21 /L (mean 23.7 by 18.1 u), and sporocysts are 12 to 15 by 7 to 9 A (mean 13.6 by 7.5 4). A polar granule is present, but an oocyst residuum is absent. Prepatent and patent periods averaged 3.3 and 4.7 days, respectively. The ovoid oocysts of I. hammondi measure 24 to 30 by 16 to 21 ,u (mean 27.1 by 18.9 a/), and sporocysts are 13 to 18 by 11 to 15 A (mean 16.0 by 11.9 I/). The oocysts lack a micropyle, oocyst residuum, polar granule, and Stieda bodies. Prepatent and patent periods averaged 5.3 and 3.5 days, respectively. This is the first report of prepatent and patent periods of an Isospora species from a rodent. Nineteen marsh rice rats, Oryzomys palustris (Harlan), were trapped in the Tuskegee National Forest, Macon County, Alabama, and examined for coccidia at the Regional Parasite Research Laboratory, ARS, USDA, Auburn, Alabama. Nine of these animals harbored coccidian oocysts. Two species of coccidia were distinguished-one of the genus Eimeria and one of the genus Isospora. Both are previously undescribed and are described herein as new