An extension of the electrochemical shear-rate measurement technique is carried out in this work to evaluate the friction force and the shear stress on a particle in two and three phase fluidized beds. Using this technique, the skin friction on a sphere has first been validated for single phase flow. In two- and three-phase fluidized bed, the significance and the direction of the velocity gradient at the wall are discussed. In the case of three phase fluidization, glass spheres (2 mm in diameter, p(s) = 2532 kg m(-3)) and plastic spheres (5 mm in diameter, p(s) = 1388 kg m(-3)) were used. This choice provides very different bubbly flows due to different balances of coalescence and break-up of bubbles. The contribution of the frictional force is more important in "coalescent" fluidized beds than in "break-up" fluidized beds. The effect of gas injection is depending on the fluidized particle effect on bubble coalescence and break-up. Correlations have been developed linking frictional force to gas hold-up. The correlations recommended for frictional force in fluidized beds for both systems, (i.e., coalescence and break-up) are as follows: Glass spheres (2 mm diameter, coalescence regime): F = 2.43 Re(0.052)epsilon(g)(0.4), standard deviation = 6%. Plastic spheres (5 mm diameter, break-up regime): F = 0.123 Re(0.3)epsilon(g)(0.1), standard deviation = 4%. F is a dimensionless force defined by F = F-f/P-a, where P-a is the effective weight of the sphere. In the case of inverse fluidization, where the solid phase consisted of expanded polystyrene particles 5 mm in diameter (p, (350-550) kg m(-3)), the average frictional force remains almost unaffected by gas injection due to opposite effects on terminal particle velocity and on turbulence. (c) 2005 Elsevier Ltd. All rights reserved.