Stress proteins of the Hsp70 family induced in the blue mussel Mytilus edulis exposed in the laboratory to increased concentrations of cadmium (Cd) or tributhyltin (TBT) were analysed using Western blotting and/or ELISA tests. Statistical evaluation of results indicated that increased concentrations of Hsp70 were detected by means of the ELISA tests as compared with control organisms in extracts from the gills of mussels exposed to both Cd or TBT (p = 0.022). Results of analysis by means of Western blotting showed no differences in the levels of Hsp70 in the extracts (p = 0.151). It was concluded that the ELISA test allowed a more sensitive detection of Hsp70 than did Western blotting.