Energy-resolved mass spectrometry (ERMS) using electrospray ionization and in-source collisional activation is a very promising approach to structural investigations of positional isomers and stereoisomers. This method was applied successfully in the case of two stereoisomeric aminoindoloquinolizidines. Comparison of electrospray/ERMS with several scanning modes including high-energy tandem mass spectrometry was made. Schematically, the high collision-energy regime led to fingerprints of both the isomers investigated but was totally insensitive to their stereochemical differences. The unimolecular dissociations of the protonated molecules monitored by various scan modes were satisfactory with regard to stereochemical differentiation, but without any control of the internal energy level of the precursor ions. In contrast, electrospray ionization provided easy and precise control of the energy deposition by varying the sampling cone voltage. Simple comparison of the breakdown curves, obtained by changing the potential difference between the sampling cone and the skimmer of the ion source, revealed the stereochemical dependence of different fragmentation pathways. These results demonstrate that the electrospray ion source represents a simple, sensitive and inexpensive method for performing low-energy collision-induced dissociation experiments and compares very well with more sophisticated methods such as tandem mass spectrometry.