Abstract: An I.V. Flow Controller incorporating an adjustable, differential pressure regulator that provides a constant but adjustable differential pressure across a fixed orifice. One end of the adjustment range provides shut-off and the other end full-flow. The adjustment range covers flow rates from zero to 250 ml/hr. At a given setting, the flow rate is independent of the total hydrostatic head height between the supply reservoir and a patient, provided the head height is greater than the pressure drop across the orifice at the maximum regulated flow rate, plus venous pressure, plus the pressure drop in the indwelling catheter.