The resistance to destruction of spores of Bacillus subtilis var. niger hermetically sealed in various polymeric films and exposed to ethylene oxide with and without relative humidity was determined. The effect of desiccation was also determined. The order of increased resistance to sterilization with regard to type of polymeric film was found to be: polyethylene equal to polyvinyl chloride, less than nylon, less than cellophane/polyethylene laminate, less than phenoxy, less than mylar/polyethylene laminate. Desiccated spores sealed in various polymeric films were much more resistant to ethylene oxide sterilization than nondesiccated spores. Relative humidity was an important factor in ethylene oxide sterilization with spores not sealed in polymeric films. However, with spores hermetically sealed in polyethylene, added relative humidity was an insignificant factor in the sterilization process.