Abstract: An infusion pump suitable, e.g., for delivering an adjustable, metered amount of a drug to a patient includes a pre-sterilized, thin-walled plastic syringe which is employed solely as a sterile inner liner for an outer, thick-walled split cylindrical clamp that is axially coextensive with the plastic syringe barrel. The required effect is obtained by inwardly squeezing the clamp against the wall of the plastic syringe until the two parts of the clamp come together to define a bore of a standard inner diameter. A plunger, which is tightly engaged with the wall of the so-deformed plastic syringe to prevent leakage of the drug, is normally driven at one of a plurality of selectable speeds by means of a gear box that is specially constructed to vary the plunger speed travel, and thereby the fluid flow rate of the drug in the syringe, in successive steps with each step being a predetermined constant fraction of the next-preceeding step.