The growth behaviour of small ammonium sulphate crystals obtained from primary nucleation in different crystallisers were Studied. The results revealed a broadening of the distribution upon growth of the crystals that is attributed to growth rate dispersion. This phenomenon was somewhat more pronounced in experiments with the fines imported from a 1100 1 draft tube baffled crystalliser compared to those generated in a 21 cooling crystalliser. This small difference in the growth behaviour between the crystals originating from the two crystallisers, however, does not allow one to reject the hypothesis that the Outgrowth of the crystals originating from either primary and secondary nucleation is identical For a small and for a large-scale crystalliser. The growth behaviour of these crystals was simulated Using a size-dependent growth model. The simulation results revealed that the growth model (Chem. Eng. Sci. 54 (1999) 1273,1283) is capable of simulating trends in the supersaturation and the median crystal size but was not able to describe the observed broadening of the crystal size distribution. (C) 2002 Elsevier Science B.V. All rights reserved.