Soybean (Glycine max L.) seedlings were grown in a hydroponic system containing nutrient solution with varying concentrations (0, 0.01, 0.5 mM) of cadmium (Cd) for a 48 h period. Roots and leaves were analyzed for catalase, glutathione reductase, and superoxide dismutase activities. Although a clear effect of Cd on plant growth was observed, the activities of catalase and superoxide dismutase were not altered significantly in the roots or leaves at all concentrations tested. Glutathione reductase did not exhibit any variation in activity in leaves, however, in roots an increase in activity was observed at 0.5 mM Cd. Catalase and superoxide dismutase isoenzymes were further characterized by analysis in non-denaturing PAGE. Activity staining for superoxide dismutase (SOD) revealed seven isoenzymes in leaves and eight isoenzymes in roots, corresponding to Mn-SOD and Cu/Zn-SOD. No Fe-SOD isoenzymes were observed. For catalase, one band of activity was observed in leaves and roots. Although no significant variation was observed in leaf tissue, in roots the 0.5 mM Cd treatment exhibited a slight increase in catalase activity. The results suggest that in soybean, glutathione reductase is stimulated by Cd in roots, to produce reduced glutathione to be used in the synthesis of phytochelatins or possibly as a response to the generation of reactive oxygen species induced by Cd.