Bacterial infections can progress to a life-threatening illness called septic shock, characterized by low blood pressure and vital organ damage. The syndrome is thought to be caused by parts of the bacteria and by the body s own immune response to the infection. A major bacterial product that interacts with the immune defenses is called endotoxin. This study will examine the body s response to endotoxin in the lungs or bloodstream. When endotoxin is given in small amounts to humans, even though it is not an infection, it triggers a set of responses that are typical of what one would see with a true bacterial infection. This allows us to study the earliest changes in molecules and cells that are involved in some bacterial infections. This type of model is safe and has been used in humans for many years to understand the body s responses during infections.