Crambe crambe is a toxic Mediterranean sponge that inhabits the sublittoral rocky bottoms, including some contaminated habitats. We investigated whether contamination by copper induced stress proteins in C. crambe and whether such stress might alter the production of chemical defenses. The monoclonal antibody used cross-reacted with two heat shock proteins (HSP) of 54 and 72 kDa. Both proteins were induced to a greater or lesser extent by copper contamination. The HSP54 accumulated more than HSP72, which, in contrast, appeared to respond faster and be less persistent. In a field experiment, we found a higher accumulation of HSP54 in individuals naturally inhabiting a copper-contaminated site than in those transplanted to this site four months earlier. In contrast, HSP72 was significantly induced only in the individuals transplanted to the contaminated site. In the laboratory, both proteins were induced by copper at 30 microg/L but inhibited at 100 microg/L. The highest mean values of HSP54 and HSP72 corresponded to the sponges, which showed the lowest mean values of toxicity. Thus, toxicity and production of HSP displayed opposite trends, which seems to indicate a preferential investment in cell repair at the expense of toxic molecules under stress conditions.