Contamination of operative wounds during surgery occurs primarily through contact and secondarily through the airborne route. Inspection and maintenance of air-handling equipment is essential, with special reference to air intakes, filters, humidifiers, and exhaust systems. Doors should remain closed to maintain positive pressure. Surgical attire for all personnel must provide for complete coverage of hair and arms. Intensive interim cleaning of all horizontal sufaces between operations is essential. The infection rate is proportional to the duration of the operation and the number of personnel in the room, and inversely proportional to the air changes per hour.