The effect of contact stiffness on the fluidization behaviour of cohesive powders is analysed using a combined continuum and discrete model for the fluid phase and particulate phase, respectively. Four systems made of particles with two values of contact stiffness (50 and 50 000 N/m) and two values of surface energy (0.37 and 3.7 mJ/m(2)) have been studied. The analysis has been carried out in terms of the coordination number, average contact forces and deformations and granular temperature. The simulation results show that for the low value of surface energy (0.37 mJ/m(2)) the contact stiffness does not influence appreciably the fluidization behaviour. In contrast, the behaviour of the systems with the large value of surface energy (3.7 mJ/m(2)) is strongly influenced by the contact stiffness: no fluidization occurs for the system with small contact stiffness and full fluidization is observed for the system with large contact stiffness. These results suggest that the influence of the contact stiffness on the behaviour of powders depends on the cohesivity of the powders: the more cohesive the powder is, the larger are the differences in the behaviour of systems with different contact stiffnesses. (c) 2006 Elsevier Ltd. All rights reserved.