Microplastics are known to be ubiquitous. It is thus not surprising that laboratory studies and field experiments demonstrated the ingestion, accumulation, cell migration and the egestion in a variety of different invertebrate species. Marine mammals as top predators are thus known to accumulate contaminants and pollutants through the food web. However, information on the occurrences and effects of microplastics in marine mammals are still scarce in the north-western Atlantic region. For revealing potential burdens, the actual presence of microplastics has to be proven. This is the first study, dealing with all three species regularly occurring in German North- and Baltic Seas: harbour porpoises (Phocoena phocoena), harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) and documents the quantity and quality of microplastics in the gastrointestinal tract. Intestine samples, whole stomachs, and faeces samples collected between 2014 – 2019 were analysed after a new established protocol of sample handling. The low share of secondary pollution and the low costs for isolating microplastic particles are significant benefits of this protocol. First preliminary results already show the identification of PE, PET, PP and ethylene-vinyl acetate copolymers by µRaman spectroscopy, and a higher share of particles compared to fibres. Up to now, the highest share of fragments (n = 28) and fibres (n= 16) was found in harbour porpoises. Whereas, the minimum of five fragments and no fibres were found in a sample of a harbour seal. The sample handling and proceeding are transferable to other mammal species, and allows new insights in predator-prey relationships. The first findings already indicate that microplastic in marine mammals from German waters is a health-relevant topic and further studies are needed.