Seabirds are regarded as a group of species with relatively low levels or even complete lack of blood parasites. We used PCR to amplify a DNA fragment from the cytochrome b gene of the parasites to search for infections of the genera Plasmodium, Haemoproteus and Leucocytozoon in individuals of two sympatrically breeding gull species, the Herring Gull Larus argentatus, the Caspian Gull Larus cachinnans and their hybrids. Out of 56 analysed individuals, 53 (95 %) were identified as infected with Leucocytozoon, whereas three individuals carried double and triple infections with at least one Leucocytozoon and one Plasmodium lineages. No Haemoproteus lineage was detected. The most common lineage (LARCAC02), for the first time reported here, was found in 51 (96 %) of all infected birds, and 14 gulls carried two Leucocytozoon lineages. We analysed the evolutionary relationship of Leucocytozoon lineages from the Herring and Caspian Gull and other bird species. Our results show that (1) the two identified Leucocytozoon lineages are not closely related as they belong to two distinctly different clusters. Moreover, (2) seabirds breeding inland could be highly infected with blood parasites and (3) this high prevalence is probably associated with areas where parasite vectors are abundant. Further studies should explore the importance of environmental factors affecting parasite prevalence, in particular within species comparisons under different environment conditions, including vector monitoring and sampling.