Two-dimensional Fourier transform (2D FT) spectroscopy was applied to ion-cyclotron resonance (ICR) to obtain direct evidence for mass transfer due to ion-mol. collisions. The 2D FT ICR expt., which is closely analogous to 2D exchange NMR spectroscopy (NOESY), yields similar information to tandem mass spectroscopy (MS/MS), but could in principle be extended to study a manifold of mass-transfer processes simultaneously. [on SciFinder (R)]