Silicon-based ceramics have been found to interact chemically with a number of metals and alloys when the materials were placed in physical contact in air at temperatures in the vicinity of 1000‡ C. Among the reaction products found after 100 h were silicides, silicates and carbides and the severity of the interaction depended on the temperature and the ease of migration of free silicon from the ceramic to the metallic phase. The occurrence of these reactions may be deleterious in applications in which silicon based ceramics and alloys are in contact for extended periods at high temperatures.