Eosinophilic chemotactic factors of anaphylaxis (ECF-A) are preformed, granule-associated peptides and polypeptides, which are released during immediate hypersensitivity reactions. Although initially described as mediators released by immunoglobulin G (IgG)-dependent mechanisms from guinea pig and human lung preparations, ECF-A is also found in rat pleural and peritoneal mast cells, human leukemic basophils, and in human nasal polyps, which contain increased numbers of mast cells. The biological activities attributed to ECF-A include selective activation and deactivation of human eosinophil chemotaxis, release of human eosinophil, granule-associated arylsulfatase, activation of the human eosinophil hexose monophosphate shunt pathway, enhancement of human and/or rat eosinophil C3b complement, IgG Fc, and immunoglobulin E (IgE) Fc receptors, and augmentation of human eosinophil superoxide production. The selective chemotaxis of human eosinophils is assessed by a Boyden micropore filter technique. The sequence of the peptides was determined by a combination of methods, including the dansyl-Edman method, carboxypeptidase A digestion, hydrazinolysis, selective tritiation, hydrolysis, and amino acid analysis and amino acid analysis after acid hydrolysis or enzymatic digestion. The solid-phase peptide synthesis method of Merrifield is used for synthesizing the two ECF-A peptides isolated from human lung. These peptides are also available from commercial sources. © 1988, Published by Elsevier Inc.