A JEOL JMS-HX110 double-focusing mass spectrometer was combined with the collision cell and spherical electric sector of a HITACHI M80-B instrument to perform tandem mass spectrometry experiments. A quadrupole lens doublet was mounted between the mass spectrometer and the collision cell to improve ion transmission into the collision cell. The detection system was also improved to expand the mass range of product ions. These improvements provided reliable spectra of high-energy electron transfer dissociation (HE-ETD) of peptides using an alkali metal target. The present results demonstrated that HE-ETD by a single collision with an alkali metal target could determine the amino acid sequence and phosphorylation site of peptides.