A method for sterilizing the interior of a diffusion restricted area by introducing a sterilant in a chamber, condensing the vapor, reducing the pressure in the chamber to revaporize the condensed vapor, and maintaining the device in the chamber until the device is sterilized. The sterilant has a vapor pressure less than the vapor pressure of water and is preferably hydrogen peroxide. The pressure in the chamber while maintaining the device in the chamber may be held constant, varied, or increased. Plasma may additionally be introduced into the chamber to improve the rate of sterilization.