Abstract: Method and apparatus for sterilizing or disinfecting objects, especially thermosensitive objects, in a closed chamber such as an autoclave. The use of such sterilizing or disinfecting takes place particularly in health institutions such as hospitals, outpatient departments, etc., as well as in the pharmaceutical industry. The sterilization or disinfection is carried in a strong oxidizing agent, which can be an organic peracid, advantageously peracetic acid in gaseous form. Sterilization or disinfection is carried out in a closed chamber, under a vacuum or at atmospheric pressure. Utilizing a vacuum increases concentration of the active agent in the chamber, so that the requisite sterilizing time is shortened. According to the procedure, the sterilization or disinfection is carried out at, e.g. 40.degree. to 50.degree. C. which also increases the concentration of the active agent, so that a short action time is achieved involving minimal thermal stress on the objects which are being sterilized or disinfected.