Mass-transfer measurements were made in a parallel plate cell equipped with baffles which produced a three-channel serpentine flow pattern and three-dimensional mass-transfer distribution effects. The entry and exit configurations were in the form of slots of rectangular cross-section. Local mass-transfer coefficient values obtained in the different channels, using surface-flush microelectrodes, reflected the complex hydrodynamics associated with phenomena such as the cell inlet and exit effects, the flow reversal effects at the baffles and preferential flow phenomena in the channels. Mass-transfer measurements obtained by averaging point measurements over various zones of the cell compared favourably with those of other workers. A hydrodynamic model of flow in the cell corresponded well to the measured mass-transfer distribution.