A commercial computer software, used to model and simulate geothermal power plants, has been investigated by comparing simulation outputs with field data of existing plants. Although most simulation results were in good agreement with the field data, the program failed when predicting the H(2)S distribution between the plant streams. The computer program has, therefore, been partly modified on the basis of pilot-scale experiments directed at investigating the H(2)S behaviour in the two main plant sections, i.e. the direct contact condenser and the cooling tower. The modified version fits the field data well and is a useful tool for assessing methods to reduce the environmental impact of releasing H(2)S into the atmosphere. (C) 2002 CNR. Published by Elsevier Science Ltd. All rights reserved.