It is becoming increasingly apparent that if one is to gain understanding of the molecular processes occurring at biological membrane surfaces, a more than superficial analysis of the phospholipids making up the membrane is necessary. This implies the characterization of the individual members of molecular species within each phospholipid class. This application describes a research project first to develop sensitive techniques using mass spectrometry and gas chromatography-mass spectrometry to qualitatively and quantitatively describe the molecular species of the phospholipid classes encountered in biological membranes. The second aspect of this proposal is to apply these techniques of phospholipid analysis in the investigation of rat mast cell plasma membranes. The mast cell is involved in immediate, hypersensitive immunological reactions which can have profound physiological effects due to the release of various chemical mediators from the cell. It is hoped that detailed description of the phospholipid molecular species occurring in normal mast cell membranes and those occurring in mast cells sensitized for an immunological reaction by the attachment of antibodies onto the membrane, will indicate the role played by the membrane phospholipids in the release of the various chemical mediators during the antibody-antigen reaction at the cellular plasma membrane.