In this study, we investigate the effects of exposure to cadmium and copper on Lymnaea natalensis and Helisoma duryi. The snails were dosed with Cd2+ or Cu2+ for a period of 96h. Snails dosed with Cd accumulated the metal significantly (P<0.05) in tissues but not in shells. Mortality was observed at approximately 1mg Cd/l of culture water. In tissues and shells of snails dosed with Cd or Cu, synergistic and antagonistic metal-metal interactions involving Cd, Cu, Zn, and Pb were observed and these may affect metal toxicity. Glutamate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase were assayed in whole snail tissue sub-cellular fractions of Cd-dosed snails. Generally, enzyme activity significantly increased at lower concentrations of Cd but decreased at high concentrations of the metal. However, mitochondrial alanine aminotransferase activity progressively declined with increasing Cd concentration. The changes in some of the enzymes' activities suggest biomarker potential.