The effects of oxidation and hot corrosion on the high-temperature strength of reaction-sintered and hot-pressed silicon-nitride-based ceramics have been investigated. A strength reduction and static- fatigue sensitivity in the temperature range 700–900°C were observed in the tests in air and in the presence of salts. Silicon-nitride-based ceramics were found to be stress-corrosion sensitive over a specified temperature interval. Sample failure at lower loads was shown to result from both corrosion-induced flaws in the ceramic's surface layer and stress-corrosion cracking. Some methods for ceramic protection against stress corrosion are proposed.