Short-term simultaneous effect of high concentrations (LC25, LC50, LC75) of heavy metal ions. (Cu2+, Zn2+, Cd2+ and Pb2+) and infection with trematode partenites Echinoparyphium aconiatum onto haemolymph of mollusk has been investigated. It was noted that low doses of toxicant (2.5 and 10 maximum admitted concentrations) have variable effect. In infected molluscs the concentration of haemoglobin decreases, while in intact ones it increases. In relation to this index, it was found, that the ion Cu2+ is highly toxic, Zn2+ and Cd(2+)--toxic, Pb(2+)--moderately toxic.