MALDI-TOF MS, a technique developed in the late 1980's, is today a routine method for detection and identification of proteins but its utilization for study of spatial structure of proteins is ever-growing.. The main approaches are detection of chemical and post-translational modifications of proteins, characterization of protein structure by proteolysis, detection of protium-deuterium ion exchange, characterization of the disulfide structure of proteins and direct detection of non-covalent complexes. MALDI-TOF is thus the technique that can replace some much more time-consuming and experimentally demanding methods but it can also afford information inaccessible by other methods.