Microturbines are, promising power sources for small scale combined heat and power (CHP) systems. However, the power output and efficiency of microturbines decreases much as the ambient temperature increases. As a remedy to minimize the performance penalty at hot ambient conditions, the injection of water or steam into a microturbine CHP system was analyzed in this work. An analysis program to simulate the operation of a microturbine CHP system was set up and validated by using measured test data. The injection of hot water, which is generated at the heat recovery unit, at two different locations inside the microturbine was predicted. The generation of steam through the same heat recovery unit and its injection at the two locations was predicted as well. All the four cases provide sufficiently enhanced power output. Injection at the recuperator inlet exhibits a higher efficiency than injection at the combustor in both water and steam injections. Steam injection provides a higher power generation efficiency than water injection on the average. The injection of steam at the recuperator inlet is most promising in terms of power generation efficiency. However, water injection at the recuperator also enhances power generation efficiency while still providing thermal energy to some extent. (C) 2009 Elsevier Ltd. All rights reserved.