The authors instilled a radioactive substance (Tc⁹⁹ sulphur colloid) into the stomachs of 15 patients receiving mechanical ventilation who also had a nasogastric tube in place.  Scintigraphic radioactivity counting was performed hourly to identify the presence of gastric contents in oropharyngeal and bronchial secretions.  Patients were studied in two positions: supine and semirecumbent (head of bed elevated 45 degrees).  At five hours gastric contents were present in the oropharynx of patients in both groups.  However, gastric contents were present in the bronchial secretions of only those patients who were in the supine position.