Sieve fractions of α-lactose monohydrate and dicalcium phosphate dihydrate, respectively, suspended in solutions of lactose, were spray dried in order to obtain products with various amorphous lactose contents. The compactibility of the samples appeared to be a function of both the primary particle size and the amount of amorphous lactose. The lactose glass was considered to form a binding layer on the particle surface area. Its efficacy was found to be determined by the size and the consolidation of the particles at lower percentages, whereas the specific properties of fully amorphous spray dried lactose, e.g. its susceptibility to water uptake and magnesium stearate mixing, were brought out especially at high percentages.