Copper (Cu) significantly inhibits the growth of radish (Raphanus sativus) seedlings, even at the concentration of 1 £gM. As far as the relationship between the growth of seedlings and peroxidase (POD) activity was concerned, the reduction of radish seedlings was correlated with the induction of cationic and anionic PODs. The data show that the increase of cationic PODs (pI 8.6 and pI 9.3) and anionic PODs (pI 5.1 and pI 3.5) activities was correlated with the rise of lignin contents in Cu-treated tissues. In our investigation, among the radish root PODs, the cationic pI 8.6 POD isozyme displayed a high affinity (Km of 57.9 £gM) for syringaldazine (an analog of lignin monomer) and the similar value of catalytic efficiency jointly with the anionic pI 5.1 POD, 0.14 £gM-1S-1 and 0.12 £gM-1S-1, respectively. The results suggest that the increase of cationic POD (pI 8.6) induced by Cu treatment might be responsible for the lignification in radish roots.