In previous publications1 attention has been called to the prevalence of pathogenic bacteria, predominantly staphylococci, in the air in the operating room. Various precautions and procedures undertaken to eliminate these organisms from the air have been described. These preliminary measures were only partly effective, the most satisfactory being rigid isolation with reduction of the number of occupants to the minimum and forced ventilation with large quantities of air free of bacteria. The lowest bacterial contamination occurred during those periods when there were the fewest carriers among the operating room personnel and the general population. Since the number of carriers could not be controlled and since isolation and ventilation were only partly effective in freeing the air of bacteria, I turned to bactericidal radiant energy as a means of sterilizing the contaminated air in the region of the operative incision and the supply tables.2 In continuation of work previously