In hot and humid tropical regions, air dehumidification is widely regarded as one of the keys to achieving a better indoor environment. This paper reports results for a passive room-dehumidifying system using an existing attic space as a chamber, wood as a desiccant material, and optimized ventilation and solar energy for system operation. Along with numerical calculations, field measurements were carried out in a test house in Japan over hot and humid summers in 2003 and 2004. It can be inferred that the wooden attic space alone had a relatively high dehumidification potential of 25 g/h m(2) of attic floor area. The fully operational system had relatively high dehumidification potential and could lower the humidity of a bedroom with an occupant by approximately 4-5 g/kg dry air during the night compared to natural ventilation. The electric coefficient of performance of the system was estimated as 15, compared with 3-5 for a typical commercial dehumidification system. Therefore, the system outlined in this study could represent a promising new passive tool for moisture control in hot and humid regions. (C) 2006 Elsevier B.V. All rights reserved.