An apparatus for delivering fluids at a precisely controlled rate which comprises a fluid dispensing component having a fluid reservoir for containing the fluids to be delivered and a reservoir fill component which can be removably interconnected with the fluid dispensing component. The dispensing component can be used for the precise infusion of pharmaceutical fluids to an ambulatory patient at controlled rates. The reservoir fill assembly is uniquely designed to accept a vial component of conventional construction which is partially received within a novel adapter subassembly that can readily be removably interconnected with the fluid dispensing component.