A model has been developed to describe the kinetics of the oxidation of phenol by oxygen using laccase (EC 1.10.3.2) from Trametes versicolor as catalyst. The model incorporates an assumption, referred to as the pseudo-steady state assumption, that at any instant during the reaction the enzyme achieves an approximate steady state distribution of its various forms around the catalytic cycle. The model was validated by comparing model predictions with experimental observations of phenol transformation and oxygen consumption over time. Excellent agreement was found between experimental data and model predictions. The pseudo-steady state assumption had the advantage of reducing the complexity of the model equations to be solved while simultaneously maintaining the model's predictive ability. The pseudo-steady state model was further simplified in accordance with specific initial conditions to provide a simplified method for the estimation of the model constants. (c) 2006 Society of Chemical Industry.