With the help of a surgical nurse and using data-processing techniques, a prospective clinical study was conducted to determine the wound infection rate in two hospitals in Calgary. The overall sepsis rate was 5.2% and the clean wound rate 3.5%. The latter is the more meaningful figure as it allows for comparison between hospitals, specialties and individuals and is a good guide for hospital morbidity reviews. The groundwork for succeeding wound infection is laid in the operating theatre, and it is believed that wound infection would be reduced more by attention to Halsted's principles than by more rigid aseptic techniques. It is estimated that wound sepsis costs the Province of Alberta 1.5 million dollars per year for hospitalization alone. This amounts to roughly $1 per person per year. The annual cost of a prospective study such as the present one is approximately $7000. This is equivalent to the cost of hospitalizing 24 patients with infected wounds for one week (at $300 per week). One dividend of a prospective study is an associated reduction in infection rate. This reduction more than pays for the cost of the program.