The experimental work reported here was undertaken with the aim of extending the available database on the condensation of steam in the presence of non-condensable gases and thereby improving the empirical input to thermal-hydraulic codes used in the design of advanced water-cooled nuclear reactors. Heat was removed from mixtures of steam and air flowing upwards through a cylindrical test section by means of a double-sided, water-cooled condensing plate. The test facility used had a degassing unit which supplied water to a boiler which, in turn, delivered steam steadily to a mixing chamber where it joined with a flow of preheated air. The mixture of steam and air was supplied to the bottom of the test section after which it flowed over the condensing plate. The condensation rate could be determined by collecting condensate over a known period of time and weighing it. The rate at which heat was removed by cooling water flowing through the internal passages within the plate could be determined calorimetrically knowing the flow rate of the cooling water and its temperature rise. A programme of experiments was completed in which the rate of heat removal from pure steam and from mixtures of steam and air in varying proportions was measured as a function of plate sub-cooling for three different orientations of the plate, vertical, inclined at 45° and horizontal.