The work presented in this thesis is primarily concerned with solving structural problems in peptides using a combination of classical chemical methods, mass spectrometry and nuclear magnetic resonance spectroscopy (NMR). Chapter One gives brief descriptions of the applications of fast atom bombardment mass spectrometry (FABMS) and NMR to the solution of structural problems in peptides. Chapter Two of this thesis describes the elucidation of the structure of vancomycin-type antibiotic, OA-7653, isolated from <i>Streptomyces hygroscopicus</i> subsp. <i>hiwasaensis</i> subsp. nov. Nishida. Chapter Three examines the interaction of vancomycin and OA-7653 with peptide cell-wall analogues, N-acetyl-D-alanyl-Dalanine and di-N-acetyl-L-lysyl-D-alanyl-D-alanine, in aqueous solutions by NMR and ultraviolet (UV) difference spectroscopy. In Chapter Four, the technique of FAB mapping was applied to study the amino acid sequence of actinidin, a proteolytic enzyme isolated from the fruit of <i>Actinidiaz chinensis</i> (commonly known as kiwi fruit). Also included in this chapter are mass spectrometric studies on model peptides to examine the conditions for accurate quantitation of phosphate content of peptides. Finally, structural and quantitation studies performed on phosphorylated peptides from the enzyme glycogen synthase are described.