Common proprietary rubber and plastic medical/surgical devices were sterilized with ethlyene oxide and aerated for eight hours at 50 C, and for 24 hours at ambient temperature, and the amounts of residuals and red cell incompatibility were then determined at these times. Aeration for eight hours at 50 C desorbed the residuals much faster than aeration for 24 hours at ambient temperatures, and the red cell incompatibility after eight hours aeration at 50 C was much less than after 24 hours aeration at ambient temperature. The red cell incompatibilities of ethylene oxide, ethylene chlorohydrin, ethylene glycol, Freon-12 and ethyl alcohol were determined using a modification of the procedure used for the other compatibility studies. This modified procedure provided a linear relationship between the agent concentration and its hemolytic activity. Ethyl alcohol, ethylene glycol and Freon-12 showed no hemolytic activity under the test conditions of this study; ethylene chlorhydrin had less than 15per thousand the hemolytic activity of ethylene oxide.