Applying the volumetric characteristics of the compressor and the equation of Stodola, formulae have been developed expressing the influence of the changes of ambient temperature on the mass output of the compressor and compression ratio in the set of gas turbine. Influence on the mechanical power and energy efficiency of the set as well as on the thermal power of the waste heat boiler has been determined too. Copyright (C) 2000 John Wiley & Sons, Ltd.