During the Bremerhaven Workshop an improved, fast and easy method for the determination of ethoxyresorufin-O-deethylase (EROD) activity in dab Limanda limanda liver was tested. The improvement involved the use of a 12500 x g supernatant instead of the microsomal fraction, thus omitting the need for long ultra-centrifugations which cannot be carried out aboard a research vessel. EROD activities in the 12 500 x g supernatant and in the microsomal suspension were well correlated. Despite its disadvantages of lower specific EROD activity, higher minimum detection limit and higher analytical variance, the 12 500 x g supernatant was used for further analysis. EROD activity in dab liver showed a spatial trend corresponding to a pollution gradient in the German Bight. EROD activity was highest at sampling sites near to the Elbe and Weser estuaries. The same trend was found in liver concentrations of PCB and lindane, but not of heavy metals and other pesticides.