The hydrodynamics of the bottom region of a CFB riser have been investigated. Experiments were performed in a 0.14-m I.D. CFB riser using FCC catalyst. The riser solids mass flux was varied between 148 and 302 kg/m(2) s and the superficial gas velocity between 3.7 and 4.7 m/s. Pressure transducers were employed to evaluate the axial profile, especially the height of the bottom zone in the CFB riser. The bottom zone itself was analyzed by means of electrical capacitance tomography (ECT). Radial solids concentration profiles, probability density distribution profiles, standard deviation profiles and frequency spectra were determined in order to quantify the bottom zone hydrodynamics. The different investigation methods are in a good agreement and indicate a core-annulus structure in the bottom zone of the CFB riser. A lean core region with a narrow probability density distribution and a small standard deviation of the solids concentration exists, while the wall region exhibits a high solids concentration with a wide probability density distribution and a large standard deviation of the solids concentration. Within the bottom zone the hydrodynamics vary little with a change in height or external solids mass flux.