Hospital-acquired pneumonia affects at least 250,000 patients in U.S. acute care institutions each year and is associated with a crude mortality of approximately 30%. Cases occur at a rate of 0.5-1 per 100 admissions, constituting 10-15% of all nosocomial infections and directly accounting for approximately one-third (10%) of the total mortality. It is likely, therefore, that nosocomial pneumonia represents an important cause of death. No recent large-scale study has systematically examined the true bacterial etiology of hospital-acquired pneumonia utilizing reliable techniques that bypass the oral flora. In the absence of such data, the current approach to therapy based on the examination of sputum is not optimal. Studies that focus on pathogenesis point to the stomach as an important reservoir of infecting organisms. Recent studies suggest that rates of pneumonia can be reduced either by selective decontamination of the digestive tract with antibiotic prophylaxis or by utilizing stress ulcer prophylaxis, which maintains normally low gastric pH. It seems that the time is propitious to examine prehospital determinants of nosocomial infection, with the goal of further preventing these life-threatening events in the hospital.