A method of sterilizing intermittent positive pressure ventilators is described, using 10 per cent ethylene oxide in 90 per cent carbon dioxide. This method can be used for any type of machine available, and several different methods are described to suit the variety of ventilators. Essentially, ethylene oxide is introduced into a large bag enclosing the ventilator, which is allowed to cycle for up to 24 hours. The bag is made of Terykne, proofed with Neoprene to prevent diffusion and dilution of the gas. A simple chemical method of monitoring the process is also described.