The information that has been accumulated in recent years about metabolism and function of eicosanoids in the liver does not yet allow the presentation of a comprehensive picture. It suffices, however, to attribute to these mediators an important role in signal transduction between the different cells of the liver, especially in inflammatory reactions, in immunologic disorders, and in septic shock. Much knowledge has been gained in recent years about the biochemistry and physiology of eicosanoids in many other tissues; the methodology of the analysis of eicosanoids, their metabolites, and their cellular functions is rapidly improving. This will assist in the elucidation of the signal functions of arachidonic acid derivatives in the liver.