The family of known essential fatty acid metabolites continues to grow. Synthesis of the prostaglandins from essential fatty acids was first described by Bergstrom and Samuelsson in 1964. The thromboxanes were discovered in 1975, the pros- tacyclins, by Moncada and Vane, in 1976, and the leukotrienes by Samuelsson in 1979. The discovery of a new class of biologically active arachidonic acid metab- olites named lipoxins was announced by Bengt Samuelsson at the IVth International Spring Symposium on Health Sciences held in Washington D. C. , May 1984. This volume, Prostaglandins, Leukotrienes and Lipoxins, contains most of the papers presented in the plenary sessions of the Washington Symposium. The book is divided into six parts, each covering a different aspect of this rapidly expanding field, and contains a total of 63 chapters by an internationally recognized group of authors in each area. Part I contains 11 chapters and covers the basic biochemistry and enzymology of prostaglandins, leukotrienes, and lipoxins. Chapter 1 by Professor Samuelsson details the discovery of lipoxins. The enzymatic synthesis and biological activities of the first two members of this series, lipoxins A and B, are described. They appear to have selective secretagogue activity for human neutrophils. The lipoxins contain a conjugated trihydroxytetraene structure and thus differ significantly from the previously described leukotrienes and THETEs and, in contrast to these sub- stances, are derived by the integrated activity of two different lipoxygenase path- ways.