Trickle-bed reactors are used tbr a number of different reaction applications in chemical engineering processing. Among these applications hydrodesulfufization 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, in 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 of the pulsing itself need to be known. The tn~e physical mechanisms are especially important since the experimental investigations are usually camed out in experimental thcilities much below technical size. hi order to iav,'estigate the pulse i'low in irregular packings, capacitance tomogtapily 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 ~md 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 fi-om the outside, show a notl-unifonn distribution inside the packing. Due to the small diaaneter of the colmnn an influence of the walls was determined, which will not be lbund in larger size technical scale plants.