Residence time distribution experiments were carried out at high temperatures and pressure in a small-scale upflow reactor. A diluted and a non-diluted bed were tested. Middle distillates and hydrogen were used as feeds. The axial dispersion model was used to describe the liquid flow through the packed bed. The dependency of Pc and liquid holdup on feed velocity and temperature was examined. The behaviour of the beds tested at hot Row conditions is compared with that of identical beds tested at ambient conditions using toluene as liquid feed and the effect of liquid-phase properties is discussed