The methods, instrumentation, opportunities and present focus of international research efforts involving the study of proteins, glycoconjugates and nucleic acids use mass spectrometry as a primary structural strategy rather than as an auxiliary technique. Not only is there established interest in the metabolism of endogenous and xenobiotic substances, per se, but also in the fact that when particular structures are metabolized, they form reactive electrophilic intermediates which may covalently bind to macromolecules, and eventually become manifest in the cell or organism as toxicity or chemical carcinogenesis. Additional important covalent modifications involve studies of chemical and photoaffinity labeling of macromolecules, studies of substrate and large molecules (receptor, enzyme, etc.), binding sites, interactions and membrane topography. In this volume, the authors explore new methods of tandem mass spectrometry with array detection systems which provide high accuracy in identification, are far more rapid than the automated Edman sequencing devices, and have comparable sensitivity.