Current surgical practice proscribes prophylactic antimicrobial agents for clean operations not associated with a prosthesis or cardiac surgery. A large, prospective, randomized study challenged this by finding an improved outcome in hernia and breast surgery when antibiotics were given preoperatively. Serious flaws in this study mandate further investigation of the problem. Another challenge was directed at the efficacy of cefazolin in the prophylaxis of staphylococcal infections. Refinements in the definition and stratification of abdominal infection according to localization of infection, etiology, and degree of physiologic impairment have brought clinical studies of abdominal infection to a new level of sophistication and clinical validity.