A visual technique, for measuring bubble size in flotation equipments, has been developed. The technique combines bubble visualization methods with digital image processing procedures to process the information. The method uses a simple device to draw bubbles into a viewing chamber and exposes them to a monochrome CCD progressive scan camera. Visual data is captured and stored at regular intervals of time. The image acquisition and the off-line processing were automated. The new visual system was tested in a 50 1 lab scale cell, two-phase system, permitting us to characterize a large number of bubbles. The performance of the new method was studied altering the operating- and chemical conditions in the cell: impeller speed, air flow rate and frother concentration. The outcome of the experiments is compared with the results achieved using a UCT bubble size analyzer. Consequently, this paper discusses the features of the new method and tries to give a explanation to the found discrepancies between the methods. (C) 2002 Published by Elsevier Science Ltd.