In the investigation of several blood stream infections following open-heart surgery, sutures and other material that had been exposed and handled in the sterile field were examined bacteriologically. One hundred and seventy-five open-heart operations were carried out during the study period and a high percentage of the specimens cultured yielded viable staphylococci and diphtheroids. Glove powder, textile fibres, and skin squames were found in the dust that collected in the room during the operations and staphylococci were frequently recovered from this source, and from the floor. Although the air supply to the theatre appeared to be of good quality, it is suggested that air currents within the room had caused dissemination of this foreign material and had probably contributed to wound infections.