The mixture effects of arsenate and cadmium were studied in Silene vulgaris (Moench) Garcke. The results show that the toxicity of the mixtures, measured as inhibition of root elongation, increased with increasing concentrations, ranging from nonadditive or slightly additive to synergistic. The elements did not influence each other's uptake. This was as expected, considering the differences in uptake mechanisms between both elements. Concentrations of detoxifying phytochelatins (PCs) were additive, with respect to both external and root-internal metal concentrations. However, at high exposure concentrations, the plants metabolism collapsed, resulting in very low PC concentrations.