THIS BRIEF review will cover only some of the important aspects of the subject but will try to define an outline from which one can gain a reasonable concept of current knowledge and proceed to further detailed investigation if he desires. One is also directed to recent detailed reviews 1-3 which should be of considerable interest. From the time of the original stimulus (heat, ultraviolet, toxins, antigens, trauma, etc) to the restitution of normal function there is a very complicated, and for the most part unknown, series of humoral and cellular events described by the ancient term, inflammation. A mediator may be defined as an endogenous chemical agent which takes an active part in the development of the inflammatory response. We are then concerned primarily with chemical (mediator) agents which are associated with and responsible for the events occurring during inflammation. Exogenous agents which induce inflammatory responses are not