AbstractBloodfilms were collected from 491 bats representing 12 of the 15 species of British bats, from a number of sites in England and Scotland, and examined for haematozoa.Trypanosoma (Schizotrypanum) sp. were found inPipistrelluspipistrellus, Nyctalus noctula, N. leisleri, Eptesicus serotinusandMyotis brandtii, andTrypanosoma (Megatrypanum) incertumwas found inP. pipistrellus.Both subgenera of trypanosomes appear to be transmitted by the bat bugCimex pipistrelli.Gametocytes of the haemoproteidPoly‐chromophilus murinuswere found in one‐third ofMyotis daubentoniiexamined, and stages of the parasite were found in the vector, the wingless blood‐sucking fly,Nycteribia kolenatii, collected from these bats. The piroplasmBabesia vesperuginiswas found in the blood ofP. pipistrellusandMyotis mystacinus, and was the only parasite to show evidence of pathogenicity to