During 1972 and 1973, 309 blood smears were taken from 281 birds caught in Yorkshire and in Hampshire. A seasonal variation in the prevalence of blood parasites with a peak in May was observed. The percentage of birds infected in different months ranged from 3.8 to 15.9. A number of new host records for avian haemoprotozoa were found and these, together with previously unpublished results, are presented in a table which brings the check-list of known British hosts up to date. Details are given of hippoboscid flies collected from the birds.