Curly birch trees with different degrees of manifestation of wood grain figure were studied for the activity of acid and alkaline peroxidases in the phloem and xylem parts of the cambial zone during the growing season. Peroxidase activity in phloem tissues was higher than in xylem tissues in both forms of silver birch. Correlations between peroxidase activity and the intensity of cambial growth were negative. By June, when growth processes commence in the trunk, peroxidase activity dropped significantly compared with May, when cambium was not yet active. Late in July, the prolonged high temperature period resulted in substantial inhibition of cambial activity. The activity of peroxidase, both acid and alkaline forms of the enzyme, rose in this period both in the xylem and in the phloem. High enzyme activity was found only in the tissues of curly-grained trunks. Peroxidase activity in straight-grained plants did not change. Possible pathways of peroxidase involvement in the processes of abnormal morphogeny of woody plants are discussed.