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 characterize the lipoxygenase pathway. 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 other lipoxygenase products in these cells. 3. To develop a precise and sensitive assay for SRS-A.