High mass in mass spectroscopy is defined as being the region above m/z 10000. Ionization techniques, methods of mass analysis and ion detection are reviewed. A general mechanism of formation of gaseous ions from nonvolatile, thermally labile compounds is put forward. The characteristics in common to all ionization techniques are, it is proposed, the setting-up of a charge at the condensed phase/vacuum interface, and the subsequent field evaporation of ions.