The background to the development of a rotating packed bed (Higee) deaerator is described. Early experiments with single bubbles were followed by visualization tests involving a stationary tower with trays of knitted mesh ＇bubble choppers＇. A rotating system was then designed and operated to exploit the high buoyancy forces which could be generated, anti some results are presented. Very high hydraulic capacities can be achieved, so that a 400 RPM rotor capable of treating 500 m(3)/hr of freshwater and giving 4 transfer units, is ultimately expected to be only 1 m diameter and 1.0 m long. If backmixing can be suppressed then even higher mass transfer duties can be reached.