IGCC (integrated coal-gasification combined cycle) has a highly effective gas-cleaning system for purification of coal gas, and it reaches efficiency rates of over 40%. An improvement of efficiency can be effected by cleaning coal gas at higher temperatures. To examine the influence of gas-cleaning at elevated temperatures, an integrated system study was carried out for base systems and systems with hot-gas clean-up at 250, 350 and 600 degrees C. The results show that the greater part of the improvement in plant efficiency comes from the change from. wet-gas purification to dry-gas purification. For three system designs with the Shell gasification process-the base system and two systems with hot-gas clean-up at 250 and 350 degrees C-an exergy analysis was made, so that the contribution of various units to improved efficiency could be evaluated. From the exergy analysis it became clear that further raising of the gas-cleaning temperature does not significantly improve plant efficiency; this finding supports the earlier exergy analysis.