A literature review of models used to account for the observation of an apparent size dependent growth rate (SDG) of sub-150 mu m is made. Growth rate dispersion (GRD), random fluctuation growth (RF) and a fast-growers slow-growers (FGSG) manner of growth are considered. The models are discussed in terms of their relevance to the modelling of industrial crystallization processes. An empirical SDG function to describe the growth of ammonium sulphate crystals in a 970 1 draft-tube-baffled (DTB) crystallizer is derived, by measuring the growth rate of samples of sub-300 mu m crystals removed from the fines line in a 2 1 growth cell. This model is implemented in a model for the overall description df the product crystal size distribution (CSD) from the 970 1 crystallizer.