Particulate carbon and nitrogen content of surface water seston at Sylt Roads time series stations was analyzed from 1973 to 1997. Depending on the seston density 20 to 150 ml of sea water were filtered on a 2.5 cm Whatman GF/C filter using a genuine made conical strainer concentrating the seston material on a small filter area (6 mm diameter). To avoid bursting of cells and subsequent loss of material it was necessary to ensure that the filter did not run dry during this procedure. Filters were dried for 24 h at 60°C and stored in a desiccator over silica gel. For analysis the seston filled filter area was cut out, folded and transferred into a zinc cartridge which was finally thoroughly closed. For calibration purposes seven stepped amounts (0.05 – 0.3 mg) of the calibration substance (Cyclohexanone-2,4-Dinitrophenylhydrazone; C12H14O4N6) were weighed in into similar cartridges. Zinc cartridges containing 6mm diameter CF/C filter parts preflushed with 0.2 micron filtered sea water were used as blanks. A CarloErba NA-1500 Elemental Analyzer was used to determine carbon and nitrogen compounds of the samples. Within this instrument the sample is completely and instantaneously oxidised by flash combustion, which converts all organic and inorganic substances into combustion products. The combustion gases are swept into the chromatographic column by the carrier gas helium. Here the gases are separated and detected by the thermal conductivity detector giving an output signal proportional to the concentration of the mixture.