Oocysts of Eimeria natricis sp. n. and Eimeria sipedon sp. n. were isolated from 2 Northern Water Snakes, Natrix sipedon sipedon (Linnaeus), in Iowa. Oocysts of E. natricis were elongate, slightly ovoid, averaging in size 32.3 X 17.5 mum; sporocysts averaged 15.7 X 8.2 mum. Oocysts of E. sipedon were broadly ovoid averaging in size 18.0 X 15.9 mum; sporocysts averaged 12.0 X 7.4 mum. In both species, sporocyst residua were present, but micropyles, polar granules and oocyst residua were lacking.