A new experimental technique has been developed and tested to measure the interfacial velocities associated with the coalescence of small, electrolytically generated gas bubbles. The technique involves measuring, by means of a linear photodiode array, the rate of deflection of a laser-light sheet caused by the movement of a newly formed boundary between coalescing bubbles. Bubble pairs in the 500 to 1000 mum range were generated at precisely controlled rates between two parallel glass-encased microelectrodes. Correlation of data obtained on the coalescence of two hydrogen bubbles of identical size shows that the position of the interface along the coalescence plane varies with the square-root of time, in agreement with the hole expansion model advanced by Charles and Mason.2 Initial interfacial velocities are in the range of 200 to 300 cm/s. Larger numbers of such events occurring simultaneously at gas evolving electrodes will significantly disturb the fluid immediately adjacent to the electrode, thereby improving mass transport rates to and from the surface.