This paper reports results from an experimental investigation into the hydrodynamic properties of slurry bubble columns (50 mm, 127 mm and 178 mm diameters), or three-phase fluidized beds at 1 and 8 bar. A non-intrusive X-ray technique was used to measure bubble sizes. velocities and hold-up for different solid particles (38 and 67 mu m zirconia) and loadings (10-30% wt/wt) with nitrogen gas (1-9 cm s(-1) superficial velocity) and water glycerol mitures (1-6cS liquid viscosity). A comparison between a sinter plate distributor and a holed grid plate are also reported.