Inflammation has been defined formany years as the response to tissue injury and infection. We are now forced to reconsider this definition by the avalanche of reports that molecules and cells associated with inflammation are activated or expressed in high concentration in a large variety of states in the absence of tissue injury or infection. Modest increases in concentration of C-reactive protein, a circulating marker of inflammation, have been reported to be associated with an astounding number of conditions and lifestyles felt to be associated with poor health; these conditions represent or reflect minor metabolic stresses. In recent years we have learned that inflammation is triggered by sentinel cells that monitor for tissue stress and malfunction-deviations from optimal homeostasis-and that molecules that participate in the inflammatory process play a role in restoring normal homeostasis. Accordingly, we suggest that inflammation be redefined as the innate immune response to potentially harmful stimuli such as pathogens, injury, and metabolic stress.-Antonelli, M., Kushner, I. It's time to redefine inflammation.