New procedures for simulating the potential growth of cotton leaves and of cotton bolls have been introduced in the new version of the CALGOS cotton model. Potential leaf growth is modeled by the monomolecular function, with different parameters for the various leaf locations in the plant. The growth pattern of seedcotton (seed plus lint) is assumed to be different from that of the burrs. The logistic function is used for seedcotton growth, whereas burr growth is assumed to be linear until the boll reaches its maximum volume. All the parameters needed in these equations have been calibrated for cultivar 'Acala-SJ2'. Simulation runs for three levels of water stress have shown a clear improvement in the correspondence of simulated leaf area index and green boll weight with the actual measured data.