Parasitological investigations on herring gulls (Larus argentatus) and greater black-backed gulls (L. marinus) from Heligoland showed a high occurrence and abundance of the nematode species Cosmocephalus obvelatus, Paracuaria tridentate, Tetrameres fissispina and Capillaria contorta. The species specific distribution of the nematodes in distinct areas of oesophageal and stomach compartments, the morphological adaptations to their environment, as with the change of host tissue caused by heavy infestations, are the theme of the present article. The pathogenity is discussed. (German)