Pseudomonas cepacia biodegraded 2,4-dichlorophenoxyacetic acid (2,4-D) according to the following stoichiometric equation : C8H6Cl2O3 + c1O2 + c2 NH3 --> c3 CH(x)N(z)O(y) + c4 CO2 + c5H2O + c6 Cl- + c7 REIM where CH(x)N(z)O(y) represents the bacterial cells and REIM is the residual extracellular intermediate metabolites. The stoichiometric coefficients c1 to c7 were determined from C, N, O, H and Cl balances together with the experimental data on the biodegradation of C-14-carboxy-labeled-2,4-D and C-14-ring-uniformly-labeled-2,4-D. The stoichiometric equation obtained predicted satisfactorily the total oxygen consumption for and the total heat production from the biodegradation of 2,4-D for a wide range of initial concentrations from 80 to 500 mg/L.