blood samples from 159 birds of the new-world family tyrannidae (the flycatchers) from the eastern plains of colombia, were examined for haematozoa parasites, in 1999-2000. haematozoa were detected in six of 20 species. the overall prevalence was 10.1%. the most common parasites detected were microfilariae, followed by trypanosoma and plasmodium. the highest prevalence (9.6%) was found in the ochre-bellied flycatcher (mionectes oleaginea). mixed infections with more than one genus of blood parasite were rare and most infections encountered were of low intensity. the results of this study suggest an important role of ecologically diverse conditions determining composition, transmission, and prevalence of a blood parasite fauna, presumably through host interaction population density. some new host parasite relationship records are presented.