Nodularin (NODLN) is a cyclic pentapeptide hepatotoxin that is closely related to microcystins (MCs). This toxin is produced by a toxic brackish water cyanobacterium Nodularia spumigena which regularly forms blooms in the Baltic Sea. Herring (Clupea harengus) were caught every 3-4 weeks in the northern Baltic Sea between July and September 1997. Salmon (Salmo salar) were caught in the same area between March and October 1997 and from the Gulf of Riga in August 1997. The total toxin content in herring muscle and salmon liver was measured with an ELISA assay. Although there were exceptionally heavy blooms of toxic Nodularia in the Baltic Sea in summer 1997, results showed that the samples contained only very low quantities of NODLN or MC. The concentrations were a magnitude lower than those we found in the livers of Baltic flounder and cod in 1997. It seems that only insignificant amounts of NODLN or MCs accumulate in Baltic herring and salmon.