Prophylactic antibiotics are indicated in all clean-contaminated and many clean procedures, especially in view of the low complication rates seen with cephalosporin prophylaxis. They are best administered immediately before operation in a manner that insures a tissue level at the time of incision and they should target pathogens commonly associated with the specific operation undertaken. Therapeutic tissue concentrations should be maintained throughout the period of potential bacterial contamination but not beyond 24 hours after surgery. Linton has been proved corrected in predicting the contribution of preventive (prophylactic) antibiotics to surgery. They are a useful tool in the surgeon's effort to minimize the occurrence of postoperative infection. However, these agents must be used with, and cannot replace, meticulous and aseptic surgical technique. Current research providing information concerning the basic cellular and molecular bases of host defense against bacterial primary lodgment and invasion provide strong evidence that the surgical patient of the future will benefit by an extended ability to normalize natural host defenses rendering those few bacteria that gain access to the wound incapable of producing infection. At that time preventive (prophylactic) antibiotics will become less important in the control of postoperative infection.