Mass and tandem mass Spectrometric results for N‐allyl‐N′‐arylsulphonylthioureas,‐isothioureas and ‐guanidines using the pneumatically assisted electrospray (ionspray) technique are presented. The mass Spectrometric experiments show dominant quasi‐molecular peaks of the monomers and signals of dimers and, more weakly, fragments. Full mass spectra are available from amounts below 500 fmol, indicating a high sensitivity. By tandem mass spectrometry of the protonated molecular ions and their fragments (sequential dau ghter‐ion scanning) and using the chlorine and bromine isotope patterns, the fragmentation pathways were elucidated.