Bacteriological study of personnel, patients, and environment in 250 surgical procedures resulted in documentation of airborne infection during surgery. Mere presence of a disseminating carrier in the periphery of the operating room resulted in two wound infections among 169 patients exposed. No other carrier of the specific phage type responsible for the two infections was found. During 82 operations the carrier's Staphylococcus was recovered from one or more environmental cultures and from 56 on the aseptic field. During 42 operations fall-out plates in the periphery of the room showed the same organism. Air cultures taken were positive during 19 operations. It is epidemiologically significant that a disseminating carrier, conventionally masked, gowned, and shod, in any part of the operating room is a hazard to the patient.