Aqueous penetration into starch based sulphonamide tablets was reduced when surfactants were included in the formulations. This is probably due to the liquid uptake being dependant on the disruption of the tablet matrix as the volume of liquid uptake was much larger than the pore space in the intact tablet. Starch swelling also affects this penetration process. In tablets containing microcrystalline cellulose, the surfactant improved liquid penetration by improving the wettability of the tablet interior facilitating liquid access. For tablets with sodium calcium alginate, the surfactant retarded the initial uptake of liquid markedly. The strongly swelling sodium calcium alginate appeared to 'waterproof' the tablet interior when wetted. The influence of surfactant on aqueous penetration may be governed by the porosity of the tablet and the nature of the excipient (s) incorporated in the formulation.