Effusivity has recently been proposed as a process analytical technology (PAT) for monitoring the uniformity of powder blends resulting from pharmaceutical mixing processes. The objective of this work is to gain insight into the accuracy, sensitivity and limitations of effusivity as an indicator of blend uniformity. Two series of experiments were carried out. First, monitoring experiments were used to determine and compare the optimal blending times of a pharmaceutical mixture obtained by three different methods: effusivity, density and UV spectroscopy. A second series of experiments was conducted to quantify the influence of density on effusivity measurements. The potential of effusivity to be used as a tool for assessing blend uniformity is discussed. In particular, the results from these experiments reveal that the accuracy of effusivity in determining optimum blending times depends on the blend physical characteristics and is significantly influenced by density. (c) 2006 Elsevier B.V. All rights reserved.