Copper (Cu 2+) significantly inhibits the growth of radish ( Raphanus sativus) seedlings at the concentration of 1 μM. As far as the relationship between the growth of radish roots and peroxidase (POD) activity is concerned, the reduction of radish roots is correlated with the induction of cationic and anionic PODs. The data show that the increase of cationic PODs (p I 8.6 and p I 9.3) and anionic PODs (p I 5.1 and p I 3.5) activities was correlated with the rise in lignin content in Cu-treated tissues. In our investigation, among the radish root PODs, the cationic p I 8.6 POD isozyme displayed a high affinity ( K m of 57.9 μM) for syringaldazine and the similar value of catalytic efficiency jointly with the anionic p I 5.1 POD, 0.14 and 0.12 μM –1 s –1, respectively. The results suggest that the increase of cationic POD (p I 8.6) induced by Cu treatment can be a good candidate for lignification in radish roots.