A theoretical and experimental investigation of humidification-dehumidification desalination system is presented. The system is based on an open cycle for water and a closed cycle for the air stream. The air is circulated either by natural or forced circulation. The system modeling is based on various heat and mass balance equations and their numerical solution. The effect of operating parameters on the system characteristics has been investigated. An experimental test set-up has been fabricated and assembled. The set-up has been equipped with appropriate measuring and controlling devices. Detailed experiments have been carried out at various operating conditions and using several packing materials. The heat and mass transfer coefficients have been obtained experimentally and fitted in forms of empirical correlations. The results of the investigation have shown that the system productivity increases with the increase in the mass flow rate of water through the unit. Water temperature at condenser exit increases linearly with water temperature at humidifier inlet and it decreases as water flow rate increases. The higher water temperature at humidifier inlet or water flow rate, the higher is the air temperature and humidity ratio at condenser inlet and exit. A maximum productivity of 5.8 liter/h has been obtained using wooden slates packing and with forced air circulation. No significant improvement in the performance of the desalination unit has been achieved by forced circulation of air at high water temperatures. The average relative deviation of theoretical predictions from measurements is (-0.9%) in the air temperature at condenser inlet, (3.8%) in the humidity ratio at condenser exit and (-1%) in the water temperature at condenser exit. (C) 2009 Elsevier B.V. All rights reserved.