2082808 9300954 PCTABS00019 An implantable osmotically driven syringe (20) is disclosed which can be used to deliver a beneficial agent, such as a drug, at a predetermined rate over an extended period of time. A movable piston (24) divides the syringe (20) into a beneficial agent-containing compartment (23) and a driving compartment (26). The piston (24) is movable into a position wherein the driving compartment (26) has an unoccupied volume of essentially zero. The syringe (20) is driven by an osmotic engine (10) which has a shaped wall (12) surrounding, and in contact with, an osmotic solute (17). The wall (12) is comprised of a semipermeable and/or microporous material which is permeable to the external fluid (e.g., water) but is impermeable to the solute (17). The engine (10) also has a passageway (13) forming a fluid flow path between the osmotic solute (17) and the driving compartment (26). A portion of the wall (12) is exposed to a fluid-containing external environment. At least about 30 % of the wall (12) which contacts the solute (17) also is exposed to the fluid in the external environment. In operation, water from the external environment is imbibed through the semipermeable wall (12) forming a solution of the solvent (17) in the osmotic engine (10). As fresh incoming fluid from the external environment is imbibed by the engine (10), the solution is pumped through the passageway (13) into the driving compartment (26). The pumping action drives the piston (24) which causes the beneficial agent to be delivered by the syringe (20).