Scientific studies conducted during the last 10 years have resulted in a great improvement of our approach to the appropriate use of prophylactic antibiotics in the surgical patient. Errors of the past including faulty timing of the initial dosage as well as prolonged duration of prophylaxis have largely been remedied. Present studies are designed to define the patients within the various subsets of diseases or surgical procedures who are at greatest risk of infection. It is these patients who can be expected to benefit most from the efficacious use of prophylactic antibiotics as well as other preventative measures.