The effect of batch and semi-batch additions of the stoichiometric amount of H2O2 on enzymatic removal of phenol has been studied over the phenol concentration range of 1-10 mmol/L. It is found that the ratio between the maximum H2O2 concentration during the reaction and the initial horseradish peroxidase concentration ((H2O2)(max)/(HRP)(0)) controls the rate of phenol removal by horseradish peroxidase in the presence of the additive, polyethylene glycol. An optimum range of this ratio is determined to be between 10 and 25 mu mol/U. Empirical models are proposed to predict the values of (H2O2)(max)/(HRP)(0) required to treat given phenol concentrations under different modes for adding H2O2.