C o n c e n t r a t i o n s of zinc and cadmium in whole soft parts of mussels, Mytilus edulis (L.), collected from 54 locations in S c a n d i n a v i a n waters were determined. Local variations in c o n c e n t r a t i o n s of the two metals found in samples taken close to industrial sources of zinc and cadmium c o n f i r m e d the ability of the m u s s e l to act as an accurate indicator of p o l l u t i o n by these m e t a l s over the entire range of salinities in which this species can exist. In addition, offshore samples remote from industrial d i s c h a r g e s r e v e a l e d higher c o n c e n t r a t i o n s of zinc and cadmium in m u s s e l s from lowsalinity areas (Gulf of Finland, S o u t h e r n B o t h n i a n Sea, Baltic proper) than in those from h i g h -s a l i n i t y areas (Kattegat, Eastern Skagerrak). Major decreases in metal conc e n t r a t i o n s present in the m u s s e l were apparent in the regions of the Sound and the Great Belt, which are areas of rapid salinity change due to m i x i n g of Baltic water with water from Kattegat. C o m p a r i s o n of these results with those reported for zinc and cadmium in water throughout the study area suggested the existence of a higher biological a v a i l a b i l i t y of these metals in regions of low salinity; p o s s i b l e reasons for this are discussed. Data from the present survey are also compared to those reported for m u s s e l s taken elsewhere. This c o m p a r i s o n reveals the Baltic area to be c o n s i d e r a b l y p o l l u t e d by trace metals; in contrast, the waters of K a t t e g a t and Skagerrak are c o n s i d e r e d to be r e l a t i v e l y unpolluted.