Conventional controlled-release products for oral administration normally lack any unique property which would facilitate drug targeting to a specific location in the gastrointestinal tract. In view of the time course of gastrointestinal transit, any slow release system having a drug release-time profile extending beyond 6 to 8 hours is likely to be present in the colon for release of a high proportion of the drug payload. If the formulation has the appropriate dissolution control, the colon capable of absorbing the drug and the half-life sufficient to achieve therapeutic concentrations, the plasma concentrations can be maintained for longer following each dose. Biopolymers are mainly plant-based polysaccharides, which are digestible by the bacterial enzymes and are almost untouched by enzymes secreted by the gut wall. As a consequence such materials, particularly those which have pronounced swelling properties, have been frequently employed in the formulation of controlled drug release products and are especially valuable as the basis for colonic drug delivery systems.