Studies of the pathophysiology of gram-negative pneumonia have been hampered by many different factors. These have included the use of small animal models, the accompaniment of anesthesia, and the problem of studying an animal at only one given point in the time course of the pneumonitis. We report here the development of a large animal model of pseudomonas pneumonia. The model allows one to study many of the pathophysiological changes associated with gram-negative pneumonia over a prolonged time frame. General anesthesia is not required. Light ketamine anesthesia was employed during the insertion of monitoring lines and during the endobronchial instillation of bacteria. During both of these procedures the animals were able to breathe spontaneously and no periods of respiratory depression or hypotension were observed. Once pneumonia was established, no sedation of any kind was required. Thus the model appears to have clinical relevance.