In orthopaedics where a great number of implants are in use, the chance for infection is high. To keep up the aseptic condition and giving antibiotic in the perioperative time is necessary. According to the effect on postoperative bleeding authors did compare two second generation cephalosporin, the cefamandol and the cefuroxim, which are mainly used in antibiotic prophylaxis. The gamma carboxylation of glutaminic acid is inhibited by cefamandol in the liver, which is necessary in the prothrombin synthesis. The cefuroxim is without any effect on prothrombin synthesis. The postoperative bleeding was significantly higher following cefamandol administration. According to the authors in orthopaedics, where the blood loss could be high, that type of antibiotic prophylaxis is recommended, which has no effect on bleeding.