Experiments are presented in which electrical-impedance tomography (EIT) and gamma-densitometry tomography (GDT) measurements are combined to simultaneously measure the solid, liquid, and gas radial distributions in a vertical three-phase flow. The experimental testbed is a 19.05-cm diameter bubble column in which gas is injected at the bottom and exits out the top while the liquid and solid phases recirculate. The gas phase is air and the liquid phase is deionized water with added electrolytes. For the solid phase four different particle classes are investigated: 40-100 mum and 120-200 mum glass particles (2.41 g/cm(3)), and 170-260 mum and 200-700 mum polystyrene particles (1.04 g/cm(3)). Superficial gas velocities of 3-30 cm/s and solid volume fractions up to 0.30 are examined. For all experimental conditions investigated, the gas distribution shows only a weak dependence on both particle size and density. The average gas volume fraction as a function of superficial gas velocity can be described to within +/-0.04 by a single curve. For most cases, the solid particles appear to be uniformly dispersed in the liquid.