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 in Pipistrelluspipistrellus, Nyctalus noctula, N. leisleri, Eptesicus serotinus and Myotis brandtii, and Trypanosoma (Megatrypanum) incertum was found in P. pipistrellus. Both subgenera of trypanosomes appear to be transmitted by the bat bug Cimex pipistrelli. Gametocytes of the haemoproteid Poly‐chromophilus murinus were found in one‐third of Myotis daubentonii examined, and stages of the parasite were found in the vector, the wingless blood‐sucking fly, Nycteribia kolenatii, collected from these bats. The piroplasm Babesia vesperuginis was found in the blood of P. pipistrellus and Myotis mystacinus, and was the only parasite to show evidence of pathogenicity to bats.