A simple two-phase model, originated from the Haldane model, was presented to predict the behavior of batch culture operations, in which the substrates show an inhibition effect on biomass growth. The model was based on the two regions of metabolic activity: the lag phase and the log phase. The validity of this model was experimentally verified with respect to the growth of freely suspended Pseudomonas putida CCRC 14365 during the biodegradation of phenol. In contrast to the one-phase Haldane model, it was demonstrated that the proposed two-phase Haldane model much better predicted the dynamics of biomass growth including the transient region from the lag to the log phases. (c) 2005 Elsevier B.V. All rights reserved.