The behaviour of the individual particles in dense gas and liquid fluidized beds and the behaviour of the jetsam particles in gas fluidized beds containing binary mixtures of different density group B powders has been observed. These visualizations have been made by means of an optical probe fitted with a conical glass cap making it possible to focus onto the particles. The individual particle mobility was observed to increase with decreasing cohesiveness and to be higher in liquid than in gas fluidized beds. The particles were seen to be in lasting contact, most of the time being largely immobile in a structure-like arrangement while being fluidized. This low particle mobility was apparent also in dry group B powders where interparticle cohesion is accepted to play a negligible role. Furthermore, the particle mobility was higher near the bottom of the bed and decreased towards the top of the bed, where the disturbances were less frequent and of larger scale. In the gas fluidized bed containing a binary mixture, heavier particles appear to be lying on a structure of touching glass ballotini. When provided with the opportunity through disturbances caused by rising bubbles they move through deficiencies and settle towards the bottom of the bed.