Microcystins (MCs) and structurally related nodularins (NODs) are hepatotoxic cyclic peptides produced by bloom-forming cyanobacteria. These toxins have been implicated in the deaths of wild and domestic animals as well as in incidents of human illness. Cyanobacterial toxins occurring in the fresh and brackish waters of the Pomeranian Province, northern Poland were characterized in this study. Water samples collected from seven lakes in August and September 2005 were analysed by high performance liquid chromatography (HPLC), enzyme linked immunosorbent assay (ELISA) and protein phosphatase inhibition assay (PPIA). Cyanobacterial toxins present in field samples and in an isolated strain of