Trickle-bed reactors are used for a number of different reaction applications in chemical engineering processing. Among these applications hydrodesulfurization and hydrotreatment are the most common. For certain operating parameters of the reactor, the flow through the packing becomes instable and the pulse flow regime is established Ln this regime, the mass transfer as well as the pressure drop is increased. In order to be able to operate commercial plants safely in this operating regime, the physical reasons for the onset and the physical properties or the pulsing itself need to be known. The true physical mechanisms are especially important since tile experimental investigations are usually carried out in experimental facilities much below technical size. In order to investigate the pulse flow in irregular packings, capacitance tomography was used. The imaging frequency of the system is 100Hz and the spatial resolution 0,1%. The investigations were performed at ambiant pressure in a 120mm diameter plant using air and water as the gas and liquid phase, respectively. The results indicate a strong three-dimensional distribution of the gas and the liquid phase inside the column. The liquid rich zones, appearing to be plane from the outside, show a non-uniform distribution inside the packing. Due to the small diameter of the column an influence of the walls was determined, which will not be round in larger size technical scale plants.