SUMMARY This paper describes an experimental and theoretical investigation of a non-traditional approach to the air humidification process that uses a hydrophobic membrane contactor acting as a porous barrier between the water and the air to be humidified. The cross-flow contactor consists of a 1.2 m2 total membrane surface of hollow polypropylene capillaries, 200 m wall thickness, arranged in a staggered array. A set of experimental results obtained with air flow-rates up to 80 m3/h outside the bundle of capillaries is presented and discussed in relation to the theoretical predictions given by a numerical model developed to predict the humidification efficiency of the contactor. Results show a good humidification efficiency of this system. The influence of the various parameters that affect vapour mass flux through the contactor is pointed out.