The toxicity of cadmium, zinc, and cadmium/zinc mixtures at concentration ranging from 100 to 10,000 microg/L was investigated against the encystment strategy of free-living metacercarial stages of the parasitic fluke Notocotylus attenuatus. Exposure of encysting cercariae caused a reduction in encystment by all metals at concentrations of 1000 microg/L or higher. The formation of cyst associations was reduced in all metal-polluted test solutions. In addition, there was an increase in the number of floating metacercariae (cysts formed when not in contact with any surface) at low metal concentrations. The effects of metal toxicity to encystment strategy and its influence on transmission to the target host are briefly discussed.