Specific mechanisms of recognition of microbial products have been developed by host cells. Among these mechanisms, recognition of lipopolysaccharide of Gram-negative bacteria by CD14, a glycoprotein expressed at the surface of myelomonocytic cells, plays a major role. There is increasing evidence that CD14 also serves as a receptor for other microbial products including peptidoglycan of Gram-positive bacteria. A common theme is that CD14 represents a key molecule in innate immunity. Recognition of microbial products by host cells leads to cell activation and production of a large array of mediators that are necessary for the development of controlled inflammatory processes. When the activation process is out of control, such as in septic shock, these mediators can be detrimental to the host.