A searching study of hospital infections showed that blankets, shoes, the bottoms of trousers, straw brooms, dry mops, and certain types of vacuum cleaners were important spreaders of infection. It was found that the surgical area could be cleaned up and would remain clean until contamination was introduced. Personnel could learn so to conduct themselves with respect to masks, clothing, and shoes that they would not introduce contamination. An interchange zone was developed to separate the surgical area from uncontrolled areas, and a sexless, sizeless, reversible gown and improved footwear were adopted to facilitate changing when personnel are obliged to pass from one area to another. A fitted filter autoclavable mask was devised to prevent contamination of clean room air by respiratory exhalations of personnel or patients. If deep-seated wound infections with resultant systemic manifestations are to be prevented, the ultimate in asepsis must be attained, and no leniency can be tolerated.