The growth rates and growth rate dispersion (GRD) of four different faces of alpha-lactose monohydrate crystal were measured at 30, 40 and 50 degrees C in the relative supersaturation range 0.55-2.33 in aqueous solutions. The overall growth rate of the crystal is around 50-60% of the (010) face of the crystal. The power law was applied to the growth rates of the four faces and the activation energies were calculated to be between 9.5 and 13.7 kcal/mol. This indicates a diffusion-controlled growth, but the exponents calculated are between 2.5 and 3.1 which are higher than unity. Introduction of critical supersaturation decreased the exponents to between 1.8 and 2.4. The variance of GRD for the (0 10) face is twice the variance of the GRD of the (110) and (10 0) faces and 10 times higher than the (1 (1) over bar(1) over bar) face at the same supersaturations and temperatures. The GRID of the four faces were similar when expressed as a function of growth rate. However, the (011) face displayed lower GRD than the other faces at the same temperatures and supersaturations. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.