The relative extent of crystallization for lactose and sucrose within spray dryers allows the WLF equation to be tested for this type of in-process crystallization, since this equation suggests that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature of that particular material. The material temperature is most strongly influenced by the gas temperature, although the particle drying behaviour is also important, while the glass-transition temperature is affected by the material composition and the particle moisture content. In this study, sucrose crystallization rate was studied using a bench-top spray dryer (Buchi B290) over a practical range of inlet gas temperatures (95-220^oC). It has been found that very large changes in the degree of crystallinity for the final spray-dried product can be achieved for sucrose by using different inlet gas temperatures, compared with much smaller changes in the crystallinity of lactose for a similar range of inlet temperatures. This result supports the suggestion that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature, since sucrose has a much lower glass-transition temperature (62-67^oC) than lactose (101^oC). The results have the potential to be implemented to achieve specified degrees of crystallinity in many powder materials produced from spray-drying processes.