Organotin compounds including methyl- and butyltin species were determined in selected aquatic specimens (fish muscles, fish liver, mussels, algae) as well as in sediment and water from the mud flats of the German North Sea and the River Elbe. The concentration of tributyltin (TBT) ranged between 27-202 ng/g (fresh mass) in fish muscles, 54-223 ng/g (fresh mass) in fish liver, 10-25 ng/g (fresh mass) in common mussels and 42-97 ng/g (fresh mass) in bladderwrack. The concentration of total organotin compounds (mono-, di-, and trimethyltin + mono-, di-, and tributyltin) in water samples along the River Elbe up to the Elbe estuary ranged between 30-96 ng/l. Retrospective investigation of butylin compounds in mussel samples from the North Sea was performed by the analysis of cryogenically stored samples from 1985. A comparison of the results with that in muscles from 1993 shows that the total tin content and the TBT content decreased from 1985-1993 by a factor of 3.5 and 6.5, respectively. In addition estimated bioconcentration factors (BCF) for organotin compounds in samples from different trophic levels are presented.