The dehumidification potential of a cross-flow membrane based air-dehumidification unit is analysed for tropical climatic conditions. The process of dehumidification is driven by the gradient of the concentration of water vapour between the incoming ambient air and the relatively dry exhaust air from a building. Electric energy is used for air transport only. This paper reports on experiments, physical modelling and computer simulations performed for the analysis of a laboratory-type dehumidification unit in Singapore. Experimentally moisture reductions between 4 g and 8 g of moisture per kg of moist air have been achieved for high humidity ambient air conditions (16 g/kg and 20 g/kg, respectively). Membrane dehumidification units may be used as stand-alone dehumidification units or as pre-dehumidification devices in the context of more complex air-conditioning systems in tropical climates.