Epidemiological investigations were carried out in a focus of opisthorchiidosis in Brandenburg state of Germany. 9 out of 23 cats harboured adult flukes in their livers. Beside Opisthorchis felineus, Metorchis bilis was found in 4 cats. Muscle samples of 227 cyprinid fish belonging to 6 species (Rutilus rutilus, Scardinius erythrophthalmus, Alburnus alburnus, Abramis brama, A. ballerus, Blicca bjoerkna) were examined for trematode metacercariae. 12 different types of cysts were found. O. felineus was present in all fish species. R. rutilus and A. alburnus showed a prevalence of Opisthorchis of more than 70%. Two out of 166 Bithynia leachi were positive for trematode developmental stages. Due to their young age the rediae could not be specified.