Combined cycle power plants consist of a gas cycle, which uses gas turbines to generate electricity, and a water-steam cycle, which uses steam turbines to generate electricity. In gas turbine power plants, operation performance is the function of ambient air temperature, pressure, and humidity. Electricity consumption increases in summer seasons due to increasing cooling demand to satisfy thermal comfort conditions. Ambient air temperature affects gas turbine power output and peaking problem occurs at higher temperatures in the electricity grid. Inlet air cooling is a method to increase the power output of a gas cycle by decreasing the temperature of inlet air to the cycle. Inlet air cooling in gas turbine power plants can be obtained by the evaporative cooling method, fogging, absorption, and mechanical compression chillers mainly. Evaporative media or fogging system increases the relative humidity up to 95 per cent and as a result inlet air temperature decreases and mass flowrate to the compressor increases. In this study, a combined cycle power plant is considered with a fogging system and a parametric study is performed to analyse the effects of the ambient temperature and the humidity on the combined cycle performance. When a fogging system is applied to the cycle, the net power generation and the net fuel input of the combined cycle are increased by 8.3 per cent. Besides, plant auxiliaries and water consumption is also increased by 0.55 per cent and 4.2 per cent, respectively. However, energy and exergy efficiencies are decreased by 0.2 per cent in the case of applying a fogging system.