Abstract
After lethal irradiation with γ-rays, mice contaminated with Enterobacter cloacae died earlier than expected. Pseudomonas aeruginosa, which is the usual cause of unexpected early radiation deaths, was not detected in dead mice. Evidence of an E. cloacae bacteraemia was obtained in irradiated mice and it is concluded that contamination with E. cloacae is a potential hazard in experiments involving measurements of radiation lethality.