Introduction. Infection is disastrous in arthroplasty surgery and requires multidisciplinary treatment and debilitating revision surgery. Between 80-90% of bacterial wound contaminants originate from colony forming units (CFUs) present in operating room air, originating from bacteria shed by personnel present in the operating environment. Steps to reduce bacterial shedding should reduce wound contamination. These steps include the use of unidirectional laminar airflow systems and the introduction of theatre attire modelled on this principle (e.g. total body exhaust suits). Our unit introduced the use of the Stryker Sterishield Personal Protection System helmet used with laminar flow theatre systems. This study compares an enclosed helmet system used with standard gowns, with standard hood and mask attire. Method. 12 simulated hip arthroplasties were performed, six using disposable sterile impermeable gown, hood and mask and a further 6 using a Sterishield helmet and hood. Each 20 minute operation consisted of arm and head movements simulating movements during surgery. Air was sampled at wound level on a sterile draped operating table using a Casella slit sampler, sampling at 700l/minute. Samples were incubated on Blood agar for 48 hours at 37°c and the CFUs grown were counted. Results. Mean number of CFUs for the helmet was 9.33 with hood and mask attire having 49.16 CFUs (S. Ds 6.34 and 26.17; p value 0.0126). In all cases a coagulase negative staphylococcus was isolated. Conclusion. Although the sample size was small, we demonstrated a fivefold increase in the number of CFUs shed when using hood and mask attire compared to personal helmet and sterile hood. We conclude that the helmet system is superior to non-sterile hood and mask at reducing bacterial shedding by theatre personnel