The rate of dissolution of lactose into wafer has been shown to be controlled by two different mechanisms, depending on the final concentration of lactose required. If concentrations above the alpha lactose solubility limit are required then the dissolution rare is governed by the first order kinetics of the mutarotation reaction from alpha to beta lactose. At typical room temperatures this reaction is so slow that the rate of dissolution of alpha lactose into solution and the I ate of mass transfer away front the surface can be considered instantaneous. At lactose concentrations below the alpha solubility limit, the initial assumption that the rate of mass transfer from the surface to the liquid controlled dissolution, has been shown to be incorrect with experimental dissolution times being much longer than those predicted using a model with the lowest possible mass transfer co-efficient and an instantaneous dissolution of lactose at the surface of rite crystal. To account for this discrepancy, a model was proposed that assumed a first order reaction for the dissolution occuring at the surface. Appropriate empirical parameters were fitted to the experimental data at different temperatures and initial particle sizes, it was concluded that the surface reaction of unbinding the bound lactose molecules from the crystal structure controls the rate of dissolution of alpha-lactose monohydrate crystals below the alpha-lactose solubility, limit at temperatures below 50 degrees C. The Arrhenius constants of E-s = 37 +/- 3 kJ mole(-1) and A(s) = 152 (43-540) m s(-1), Mere determined.