The haemolytic activity of CuSO4 (0.3 mM) in vitro was reduced in the presence of albumine (5-20 g/l). The presence of D-penicillamine, triethylene tetramine or dimercaptosuccinic acid (0.3 mM) also reduced the copper-induced haemolysis, whereas 2,3-dimercaptopropane-1-sulphonate increased the cytolysis. N-ethylmaleimide (NEM) in appropriate concentrations (1 mM), as well as chromic chloride (0.3 mM), reduced the copper-induced haemolysis. Higher concentrations of NEM (2 mM) were ineffective. The results may provide helpful suggestions as regarding the clinical treatment of copper poisoning and Wilson's disease. The results may also be helpful for the understanding of the mechanisms of haemolysis associated with copper intoxication in vivo.