Metallothioneins (MTs) from digestive gland of freshwater bivalve mollusc Anodonta cygnea, exposed to 10 or to 200 microg x l(-1) copper ions during 14 days, were resolved using subsequent gel-permeation and ion-exchange chromatography on MT-1 and MT-2. In both groups of treated molluscs the content of copper in MT-2 was elevated twice. The significant elevation of this isoform, which is minor in control animals, and the increasing of the zinc level in it were also observed after treatment with 10 microg copper x l(-1). It was accompanied with Cu,Zn-superoxide dismutase (SOD) activation. Under the treatment with the 200 microg copper x l(-1) the zinc in MT-2 was at the control level, the inhibition of Cu,Zn-SOD but activation of Mn-SOD was revealed. The properties of MT-1 in all cases were similar.