Experiments were conducted to study the hydrodynamics of a three-phase jet-loop-reactor with liquid as a continuous phase. By using a perspex flow channel with a special geometry and different optical measuring systems the simultaneous measurement of the flow field as well as of the movement of bubbles and solids in three-phase flows was possible. In order to measure the distribution and movement of fine, suspended solids (rho(solid) = 2400 kg/m(3), d(p) =150 mum; 500 mum) within the bubble wakes, a specific fraction of particles was coated by a fluorescent dye. This made it possible to track single particles even at solid concentrations up to 10% by the use of an optical filter. The results indicates that the rise velocity of bubbles in three-phase flows depends on the accumulation of solid particles in bubble wakes due to the inertia of the solids. Particles which are able to follow the wake structure will increase the mass force acting on a bubble due to a higher suspension density of the wake with the consequence of a lower relative velocity. The decrease in relative bubble velocity influences the pressure drop and circulation velocity on loop reactors. Based on the measured results and the analyses of the forces acting on the bubble a model was developed which predicts the relative bubble velocity reasonably well.