Effects of various organic solvents and polyethylene glycol (PEG) on the secretion of peroxidase from carrot hairy roots were investigated. The peroxidase activity in culture broth was significantly enhanced without adverse effects on root growth when PEG was employed while other organic permeabilizing agents exerted harmful effects on root growth. PEG with a molecular weight of over 6,000 g/mol enhanced the secretion of peroxidase dramatically. Since PEG did not induce the formation of pores in the root cell membrane as confirmed by staining using Neutral Red, it was thought that the mechanism of secretion enhancement of peroxidase by PEG is different from that of other organic solvents which make the cell membrane permeable. Since PEG does not adversely affect the root growth, PEG can be applied to the repeated use of root cells for production of peroxidase.