The radioactive tracer technique was applied in a flotation column (0.91 m diameter and 12 m height) in order to compare the hydrodynamic behaviour of the liquid and mineral phases. Experiments were carried out by marking the liquid and non-floatable solid in three size classes (-38; -75+38; -150+75 μm). The mean residence time and the degree of mixing of the liquid and solid per size class was evaluated. A 2:1 ratio between residence time of liquid (or fine particles) and coarse particles was measured. It was shown that the solid dispersion number is similar to the liquid dispersion number. The effectiveness of the froth preventing the entrainment of fine particles was directly observed around the pulp/froth interface, using fine non-floatable mineral as the tracer. © 1992.