Examination of the rectal contents of 252 wild coypus, Myocastor coypus, revealed oocysts of five species of the genus Eimeria. Of these, E. myopotami and E. nutriae have been recorded from England previously, whereas E. coypi and E. seideli are recorded for the first time. A further species, E. fluviatilis n.sp., has sporulated oocysts measuring 16.5×19.0 μm, structurally dissimilar from those previously described from coypu. A revision of Eimeria of the coypu is presented which draws attention to the existence of synonymy in previous descriptions. ac]19830416