The effect of cadmium on microsomal membrane-bound peroxidases and their involvement in hydrogen peroxide production was studted in barley roots. One anionic and two cationic peroxidases were detected, which were strongly activated by Cd treatment. Positive correlation was found between root growth inhibition and increased peroxidase, NADH oxidase activity and H2O2 generation in root microsomal membrane fraction of Cd-treated barley roots.