Glutathione S-transferase (GST) and heat shock proteins (hsps) 40, 60, 70 and 90 were determined by immunoblotting using actin as an internal control in Mytilus edulis from one station outside (site1) and three stations within (sites 2-4) Cork Harbour, Ireland. Comparisons were made between gill and digestive gland and between sites. Gill shows generally higher hsp 60, 70 and 90 while digestive gland has higher hsp 40. Site I showed higher gill hsps 40 and 70 than sites 2-4 while gill GST was higher in sites 3 and 4 than I and 2. Comparison with sites in the North Sea (site 5: outside Tjarno in The Koster archipelago in the Skagerack) and Baltic Sea (site 6: Asko island) also revealed lower hsps 40 and 70 in site 6 (low salinity) than site 5 (high salinity) although hsps 60, 70 and 90 were detectable in digestive gland unlike sites 1-4. Previously, only hsp 70 had been studied at these sites [Mar. Environ. Res. 39. (1995), 181]. At the mRNA level, gill hsp 70 is 80-fold higher at Tjarno than Asko. These data suggest that, while salinity may slightly decrease hsp 40 and 70, both hsp 70 and GST are selectively up-regulated by approx. 10- and 3-fold, respectively, at Tjarno compared to the other sites which we attribute to exposure to more widely fluctuating pollution levels. (C) 2003 Elsevier Ltd. All rights reserved.