Health institutions in the framework of their activities must not only treat, but also improve the health of every man. A multitude of adverse situations in which patients may become victims may be avoided by a different approach and giving more importance to knowledge and implementation of the basic principles of asepsis and antisepsis. Sterilization is an important step in the infection control protocol. Inadequate sterilization is an important cause of exogenously acquired infections. Rates of surgical site infection differ in different studies, varying from less than 1 to over 9 per 100 procedures. Surgical site infections along with urinary tract infections and respiratory tract infections are most commonly encountered hospital aquired infections. Several international and national bodies, like Center for Desease Control and Prevention, World Forum for Hospital Sterile Supply and Croatian Association of Sterilization, have recommended regular use of biological indicators as a process control tool. Biologic indicators are ideal monitors of sterilization process because, unlike chemical indicators, they measure the sterilization process directly by using of spores and their destruction. Ineffectivness of the sterilization process could be caused by many problems such as trapping of air, wet material, faulty pressure gauge, overloading of drums or inadequate holding time. This problems could arise because of faulty autoclaves or inadequately trained stuff. Geobacillus stearothermophilus spores are used for control of the steam sterilization process. Regular use of biologic indicators is contributing to the provision of quality health care and the prevention of the occurence of nosocomial infections.