IT IS ACCEPTED and current practice in orthopedic surgery to apply towels or other sterile material to wound edges during an operation. These sterile towels, clipped securely to the edges of the wound, are presumed to diminish the chances of wound contamination and, hence, of wound infection. At the Wadsworth General Hospital, Los Angeles, it was decided to test this concept. METHOD Every major "clean," noninfected operation for a four-month period in 1953 was subjected to a study by wound culture during the progress of the surgical operation and by follow-up study of the incidence of infection. Operations were performed by some operators using towels and towel clips securely fastened to the wound edges and by others with no toweling whatsoever. Preparation of the skin previous to the surgery in all operations was identical. A sterile swab was placed into the wound immediately after the incision was made, and a