Nodularins are cyanobacterial hepatotoxins, which may cause intoxication at very low exposure levels. The nodularin-producing cyanobacterium Nodularia spumigena usually forms massive blooms in much of the Baltic Sea during the summer season. Breast feathers and liver samples from common eider (Somateria mollissima) were analysed for nodularins by liquid chromatography-mass spectrometry (LC-MS) and enzyme-linked immunosorbent assay (ELISA). Fifteen eiders from the western Gulf of Finland were caught by hunters between June and September 2005. Blue mussels (Mytilus edulis), a dietary component of the birds, were also obtained by diving near the same marine area and time as the collection of the ducks. Eider breast feathers contained 6-52 μg nodularin-R (Nod-R)/kg dry weight (dw) by ELISA, and 8-43 μg Nod-R/kg dw by LC-MS. No Nodularia filaments were adhered to feather samples according to light microscopy assessment. Liver samples from the same individuals contained Nod-R between 3 and 48 μg/kg dw by LC-MS. Mussel samples from the area contained Nod-R at concentrations of 12-80 μg/kg dw by LC-MS. Analysis of bird feathers offers a facile and non-invasive means of assessing the exposure of birds to nodularins.