Solid exchange between the bubble wake and the emulsion phase in a gas-fluidised bed was studied both experimentally and theoretically. Measurements were made on the tracer particle concentration profile produced after a single bubble passage in a two-dimensional bed, and the solid exchange coefficients were estimated with the results of simultaneous measurements on the shape, the size and the rising velocity of bubbles. A simple model for the exchange was developed on the basis of an assumption that the exchange rate is proportional to both wake volume fraction and solid flux into the front surface of the gas cloud. Experimental values of the exchange coefficient were then compared with those predicted by the model and a reasonable agreement was shown between them for a range of bubble diameters of 6 to 17 cm. The model was extended to the ordinary three-dimensional bed and the exchange coefficient was correlated with the axial dispersion coefficient according to van Deemter''s and our models.