Abstract: Automatic parenteral infusion equipment for safely delivering, under substantially constant pressure and at a substantially constant rate of flow, infusion liquid to a patient's body. The apparatus includes a chamber for containing the infusion liquid, a pressure force remote from the infusion liquid chamber, a force transmission means interposed between the pressure source and the infusion liquid chamber, vent means to discharge compressible or incompressible fluid used as a force transmission vehicle in order to prevent the possibility of embolism or toxicity to the patient, and flow regulating member including a restricted orifice to deliver infusion liquid to the patient at a substantially constant rate. Alternative embodiments of the invention are disclosed for adaptation to both ambulatory and immobile patients.