Dogs were subjected to tracheostomy and intubation with low pressure cuffed tracheostomy tubes. Various mixtures of bile, gastric secretion and 0-1 N Hydrochloric acid were injected into the trachea via a small catheter attached to the main tracheostomy cannula to simulate the effect of aspirated gastric contents. Bronchoscopic observations were made during the study to investigate the local effects of secretions pooling above the cuff, in contact with the tracheal wall. Gross pathological changes were observed when the animals were sacrificed at the end of the study. The constituents of a mixture of bile and gastric juice increased the severity of tracheal damage due to mechanical trauma and sepsis. Healing was delayed and the reparative process was abnormal. This experimental study indicates that the combination of bile and acid pepsin reaching the tracheal wall may also be a major factor which predisposes to the development of early and late tracheal injury.