The blood parasite diversity was studied in paddyfield warblers (Acrocephalus agricola) breeding in NE Bulgaria, SW Russia and S. Kazakhstan. Nine cytochrome b gene lineages were recorded, 4 belonging to Haemoproteus spp. and 5 to Plasmodium spp. The overall prevalence of haemosporidians was 33.3%. The composition of parasites varied geographically, with six lineages recorded in Russia, five lineages in Bulgaria and two lineages in Kazakhstan. Two lineages are described for the first time, i.e. ACAGR1 (belonging to Plasmodium sp. and recorded from a single bird in Russia) and ACAGR2 (belonging to Haemoproteus sp., recorded from Bulgaria and Russia). The latter lineage is the most widespread parasite in the Bulgarian population, scarce in Russia and absent in Kazakhstan. It is supposed that ACAGR2 has originated from the widespread lineage ACDUM1 differing from it by a single nucleotide. One lineage only (ACDUM2) occurs in all the three populations studied and is a nonspecific parasite known from various passerines. Six of the registered lineages have been found in a single population of A. agricola and also represent non-specific parasites occurring in a wide range of passerine birds. Their records in A. agricola may indicate the high transmission rate of these parasites in the habitats where this host co-occurs with other passerines. The variation of the composition of the haemosporidian parasite communities through the breeding range of A. agricola makes up heterogeneous selection pressures that may drive intraspecific variation in important life-history traits.