Convective diffusion theory has been utilized to describe mass transfer in an annulus under conditions of laminar flow. Rates of dissolution of benzoic acid in water were experimentally measured for values of annular core to diameter ratio, k > 0·5. The rates were consistent with theoretical predictions for values of Reynolds number, 5 < Re < 100. For Re > 100 the entrance length required for development of the fully established velocity profile was insufficient in the test system. Under the latter experimental conditions the dissolution rate increased, as qualitatively expected, over that predicted by theory.