The overall objectives of the proposal include the following: 1. To continue the study of the biosynthesis of SRS-A and other arachidonic acid metabolites in RBL-1 and normal rat mast cells. a. To investigate the subcellular localization, properties and regulation of the enzyme in the synthesis of SRS-A and other arachidonic acid metabolites. b. To determine the role of phospholipase activation in the mast cell release reaction. 2. to determine the distinct biological properties of SRS-A and to pharmacologically manipulate its action and synthesis. 3. To develop a precise and sensitive assay (radioimmunoassay) for SRS-A.