A peristaltic pump was designed for either manual or computer-controlled operations; it provides flow rates over a large dynamic range (0·01 to 30 ml/min). Driven by a stepper motor in which the stepping rate is determined manually with digital switches or under remote control, the pump is capable of operating in either direction with negative or positive back pressures, thus overcoming problems of unpredictable resistance to flow in needles and catheters through which the fluid is infused. The clamping effect of the pump rollers on the tubing prevents back flow by creating a pressure at the infusion site slightly higher than the intravascular pressures that are physiologically attainable, thus preventing clotting and microembolisation.