Compared with conventional surgical clothing, polypropylene coveralls reduced the bacterial contamination of the air of a conventionally ventilated operating room by 62%. The contamination of surgical wounds during joint replacement was also reduced, but not to a significant degree. Sixteen percent of the bacteria sampled from the wounds were resistant to the prophylactic antibiotic and the importance of a clean air system for performing joint replacement operations is stressed. The use of commercially available non-woven swabs for sampling bacteria from the surgical wound compared favourably with the use of specially prepared velvet pads.