BACKGROUND: Few data exist about buildup of secretions within endotracheal tubes of patients treated with closed-system suctioning in the intensive care unit. OBJECTIVES: To describe the extent, prevalence, and distribution of narrowing of endotracheal tubes related to buildup of secretions and to determine contributing factors. METHODS: Forty endotracheal tubes were examined within 4 hours of extubation, after at least 72 hours of use. Data on patients' daily weight and fluid balance, ventilator humidification temperatures, and nurses' descriptions of secretions during the 3 days preceding extubation were recorded. Any secretion debris in the endotracheal tubes was weighed. At 1-cm intervals along the tube, the debris was described and the depth of the debris was measured to the nearest 0.5 mm. RESULTS: Mean duration of intubation was 6.6 days. Two tubes had no debris. Mean overall depth of debris was 0.64 mm, mean greatest depth was 2.0 mm (range, 0-5 mm), and mean weight was 1.16 g. The entire tube was affected, with the greatest depth of debris at the 6- to 9-cm and 13- to 14-cm markings. Duration of intubation correlated with mean greatest depth of debris (r = 0.37, P = .02), mean overall depth of debris (r = 0.48, P = .002), and mean weight of debris (r = 0.38, P = .02). CONCLUSIONS: Endotracheal tubes are markedly narrowed by the buildup of secretions after closed-system suctioning. Duration of intubation, but not endotracheal tube size or amount of secretions, was associated with the degree of narrowing.