Infection is still a feared complication of surgery. It is known that anaesthesia inhibits the immune system but there are other steps how it may contribute to postoperative infection. An important issue in the protective process against invading bacteria is our normal skin and gut flora that may be disturbed by anaesthesia as well. We examine the impact of anaesthesia on normal flora and the effect of medications used in anaesthesia on bacterial growth. We also examine the interaction of medications used in anaesthesia with antibiotics.