A four-year experience with transtracheal aspiration was reviewed in order to determine those patients at risk for developing life-threatening complications. One hundred procedures were performed by at least 20 different physicians trained according to an established protocol. Complications were limited to minimal subcutaneous emphysema in 19 percent (10/52), pneumomediastinum in 3 percent (3/93), and gross but self-limited hemoptysis in 1 percent (one patient); occasional unifocal premature ventricular contractions were noted in one patient. We conclude that patients not at risk of developing life-threatening complications from transtracheal aspiration can be identified. They (1) are able to cooperate and have a clearly identifiable and normal cricothyroid membrane, (2) have the procedure performed only by well-trained or supervised physicians, (3) have an arterial oxygen pressure of at least 70 mm Hg with administration of supplemental oxygen, and (4) have a prothrombin activity of at least 65 percent of the control value or a normal bleeding time or a platelet count of at least 100,000/cu mm. To minimize subcutaneous emphysema or pneumomediastinum, no patient should have therapy with intermittent positive-pressure breathing or any other procedure that might induce coughing for the subsequent 24 hours.