The sporicidal activity of 2% glutaraldehyde against Bacillus subtilis var. globigii and Bacillus stearothermophilus was compared with that against Clostridium difficile. The aerobic species, normally chosen for test purposes, survived for 2 h but Cl. difficile was killed in under 10 min. In view of the impractical and lengthy immersions required to satisfy standard tests using non-pathogenic spores, a less stringent standard would probably be more appropriate.