A new method has been used to visualize particle movement and to observe the emulsion flow in a two-dimensional fluidized bed. The method is based on the ultraviolet light activation of particles impregnated with a photochromic dye solution. When activated, the particles changed their color to dark blue allowing their movement to be easily distinguished and tracked. This method enabled us to observe continuously the movement of bubbles and fine particles around a bubble in a fluidized catalyst bed. A detailed study of the particle movements around the bubbles showed that even when the bubble ascending velocity is large, the bubble is not accompanied by an upward emulsion flow. (C) 2003 Elsevier Science B.V. All rights reserved.