We investigated the effect of moisture on the high-temperature stability of several ceramics at 1700 degreesC in an atmosphere of oxygen/water vapor (O-2/H2O). The melt growth composite (MGC) which is composed of alumina/yttrium-aluminum-garnet, Al2O3/YAG, was the most stable among ceramics at 1700 degreesC in this atmosphere, showing only a slight change in microstructure, flexural strength and volume after an exposure for 200 h. Thus, MGCs are among the most promising ceramics for structural applications, at ultra-high temperatures. (C) 2004 Published by Elsevier Ltd.