Phenolic solutions were treated with hydrogen peroxide and horseradish peroxidase (HRP) resulting in more than 95% removal of phenols within 3 h. Toxic compounds were formed during the treatment of aqueous solutions of phenol, 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol and 2-methylphenol. However, the toxicities of HRP-treated solutions decreased within 21 h after the completion of the enzymatic reaction, except in the case of 2-methylphenol. The process of detoxification was significantly accelerated upon the addition of hydrogen peroxide to the dephenolized solutions. Solutions that were treated in the presence of chitosan exhibited lower toxicities than solutions treated in its absence if they were allowed to incubate for an extended period of time. Treatment in the presence of polyethylene glycol resulted in significantly higher toxicities. The toxicity of treated solutions was dependent on the addition mode of HRP and hydrogen peroxide. Treated solutions were also completely detoxified following illumination with UV light.