Abstract 1. 1. The increase in wound infection on a surgical service led to a study of possible sources. 2. 2. The infection rate has no relation to monthly admission rate, number of “dirty” cases admitted or number of operative procedures. 3. 3. Staph. aureus was present on the skin or in the noses of 49 per cent of patients and 74 per cent of the house staff. 4. 4. Blankets are a major source of contamination on the wards. 5. 5. The air of wards and operating rooms is laden with offending bacteria. 6. 6. Preoperative preparation of the skin lowers the bacterial flora but does not eliminate it. 7. 7. Silence is more valuable than masking.