The application of membrane contactors in air humidity control offers advantages over the conventional treatment methods, e.g. dew pointing by cooling (high energy consumption) and direct absorption (risk of air contamination by the absorbent). In gas/liquid membrane contactors the applied absorption liquid is separated from the feed air by a liquid tight but water vapor permeable membrane. Air and absorption liquid can be operated independently of each other and large and well-defined contact areas are provided. In the present work the properties of transversal flow modules were investigated with respect to the air side pressure drop and the water vapor transport. In order to realize a reliable prevention of leakage in long-term operation composite membranes with a thin but dense layer of PDMS were applied. Main subject of this work was the investigation of coated polyetherimide hollow fiber membranes with respect to the water vapor permeance. The measurements were carried out under actual contactor conditions using prototype modules and LiCI as liquid absorbent. The influence of both the support membranes and the coating layer as well were determined. It was shown that the negative effect of the coating on the permeance could be restricted to a permeance loss of about 20% by applying a very thin coating layer. With composite membranes based on highly asymmetric Support membranes water vapor permeances up to 0.64 m(-2) h(-1) Pa-1 could be realized. (c) 2005 Elsevier B.V. All rights reserved.