Abstract: An air handling system (10) and associated method for supplying filtered air to an operating room (14) in a manner which reduces concentrations of airborne bacteria and other particulates. The system (10) generally includes a plenum (18) mounted at the top of a first wall portion (22) of the operating room (14). A diffuser (48) is closely received in a diffuser opening (46) through which air is communicated from the air chamber (38) of the plenum to the operating room (14). The diffuser (48) is disposed so as to depend downwardly from a point proximate the ceiling of the operating room and converge toward the first end wall (22). Further, at least one air return (60) is provided at the second and opposite wall portion (54) of the operating room (14) for removing air from the room (14) and returning the air to the clean air supply unit (12). Another but smaller portion of the air is removed through at least one air return at the base of the first wall portion of the room.