AbstractThirty‐five species of protozoan parasites belonging to thirteen genera have now been recorded for British small rodents. These include species ofEntamoeba, Giardia, Spironucleus, Trichomonas, Chilomastix, EimeriaandCryptosporidiumin the gut;Trypanosoma, HepatozoonandBabesiain the blood; andToxoplasma, FrenkeliaandSarcocystisin the tissues. Recent advances have progressed along two lines, the elucidation of the life‐cycles of the species ofFrenkeliaandSarcocystis, which are now known to involve a carnivore as the final host, and laboratory studies on those parasites that can be maintained in laboratory animals. It is now possible to draw up a definitive list of hosts and parasites and this should serve as a basis for studies on the epidemiology of these parasites and their possible effects on their ho