The application of soybean peroxidase (SBP) to catalyze the polymerization and precipitation of aqueous phenols by hydrogen peroxide is potentially promising because this peroxidase is less expensive than horseradish peroxidase (HRP), which has been the focus of most wastewater research. SEP can act on a broad range of compounds and retains its catalytic ability over wide ranges of temperature and pH. Activity was optimal at pH 6.4, with significant activity observed between pH 3 and 9. SEP was very stable at 25 degrees C at neutral and alkaline conditions but experienced rapid inactivation below pH 3. SEP underwent biphasic inactivation by hydrogen peroxide in the absence of a reductant substrate. SEP was most effective when used to treat phenolic solutions between pH 6 and 9. In comparison with HRP, the activity of SEP was only slightly more sensitive to pH, was more stable at elevated temperatures, and was less susceptible to permanent inactivation by hydrogen peroxide. However, SEP was catalytically slower than HRP and a larger molar quantity of SEP was usually required to remove a given quantity of phenolic substrate.