Phenol biodegradation in a batch reactor was investigated using mixed cultures. Used cultures were able to degrade initial phenol concentrations (S-0) up to 1450 ma 1(-1). The Haldane equation was adopted in order to describe the relation between the specific growth rates (mu) and S-0(.) Kinetic constants of the Haldane equation were mu(m)., = 0. 143 h(-1), K-s = 87.45 mg 1(-1), K-i = 107.06 mg 1(-1). In simulation studies including the Haldane model, an evident disagreement was observed between measured and estimated phenol concentrations when an S-0 greater than 100mg 1(-1) was applied. The inadequacy of this model was attributed to the inhibition of metabolic intermediates of phenol degradation. A model, which has been proposed in literature for pure cultures and including the concentration of intermediates was tested for mixed cultures. This new model showed its merit in that the failure of classical Haldane model observed especially in high S-0 values was avoided. The new model gave better estimates than the Haldane model in the studied S-0 range (25-1450 mg 1(-1)). (C) 2004 Elsevier Ltd. All rights reserved.