The aim of this study was to determine the incidence, localisation and intensity of the gastric colonisation with Helicobacter-like bacteria in zoo- kept felids and to find out a relationship between type and amount of bacteria and possible inflammatory changes of the gastric mucosa. For that purpose the gastric mucosa of 186 felids was examined histologically and by immunolabelling at IZW Berlin. HE-stained tissue sections were used for the histolological evaluation of the gastric mucosa. For the immunohistochemical demonstration of the bacteria, a labelled streptavidin- biotin-peroxidase-technique combined with a commercial antibody against Helicobacter pylori was applied. The results of the bacterioscopic examination were compared with the histological findings. The clinical history and the pathological anatomical diagnosis of the post mortem were taken into account, too. The results can be summarized as follows: In 98 of the 186 felids (52,7%) from different German zoos Helicobacter-like bacteria were identified by immunolabelling. The species-specific prevalence was between 0% (leopard, clouded leopard) and 100% (certain small cat spp.). In general, gastric bacteria were more often demonstrated in older than in younger animals. In addition, females were found to be infected more often than males in the entire group of 186 cats as well as in certain species. Nevertheless, a statistically significant relation between Helicobacter infection and age or sex was not shown. Two types of bacteria were differentiated due to their morphology and localisation in the gastric mucosa. The HPLOs (Helicobacter-Pylori-Like- Organisms) were up to 4 µm long, comma-shaped and located in the mucus covering the superficial epithelial layer, in the gastric pits and in the apical lumen of the gastric glands. The HLOs (Helicobacter-Like-Organisms) were up to 12 µm long and spiral-shaped. In contrast to the HPLOs, the HLOs were also present deep within the glands and additionally in the parietal cells. Chronic inflammatory changes of varying intensitiy were found in 31 (31,6%) of the 98 gastric samples with Helicobacter colonization. The histological findings correlate with those of gastritis type B in humans which are characterized by focal to diffuse lymphoplasmocytic and lymphofollicular infiltrates. A direct correlation between the bacterial densitiy and the amount of the cellular infiltrate could not be demonstrated. HPLOs were only found in lions and tigers and were nearly regularly associated with inflammatory gastric changes. HLOs, on the other hand, were found in all feline species except leopards and clouded leopards. Marked inflammatory changes, however, were only seen in cheetahs. Helicobacter infections were found to be associated with gastrointestinal symptoms (according to anamnesis) and gross gastric changes (according to the autopsy records) only in a few tigers and cheetahs. In two tigers with the clinical symptoms of "tiger disease" HLOs were retrospectively demonstrated in the gastric mucosa. In summary, it can be concluded that bacteria of the genus Helicobacter are widely distributed in zoo-kept felids. At least in cheetahs, tigers and lions are these infections associated with subclinical chronic gastritides, in cheetahs and tigers also occasionally with clinical gastrointestinal symptoms. The question as to a causal relationship between certain Helicobacter species and special clinical syndromes (e.g. tiger disease) can only be answered by further pathological studies in combination with clinical, microbiological and molecular genetic investigations.