Electron transfer through gas phase ion-ion reactions has led to the widespread application of electron- based techniques once only capable in ion trapping mass spectrometers. Although any mass analyzer can in theory be coupled to an ion-ion reaction device (typically a 3-D ion trap), some systems of interest exceed the capabilities of most mass spectrometers. This case is particularly true in the structural characterization of glycosaminoglycan (GAG) oligosaccharides. To adequately characterize highly sulfated GAGs or oligosaccharides above the tetrasaccharide level, a high resolution mass analyzer is required. To extend previous efforts on an ion trap mass spectrometer, negative electron transfer dissociation coupled with a Fourier transform ion cyclotron resonance mass spectrometer has been applied to increasingly sulfated heparan sulfate and heparin tetrasaccharides as well as a dermatan sulfate octasaccharide. Results similar to those obtained by electron detachment dissociation are observed.