The mass spectrometric characterisation of ruthenium carbonyl-porphyrin complexes and the corresponding porphyrins is described. Matrix-assisted laser dcsorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), Past-atom bombardment mass spectrometry (FAB-MS), in both lon -resolution (LR) and high-resolution (HR) modes, and field desorption mass spectrometry (FD-RIS) have been used and compared in detail. MALDI-TOF-MS turned out to be ideal for rapid screening of potential synthetic pathways. FAB-MS proved to be especially useful in establishing elemental compositions bg HR measurement, Whereas the porphyrins gave very good molecular ion intensities, the ruthenium carbonyl complexes exhibited abundant carbon monoxide (CO) loss in MALDI-TOF-MS and still a measurable CO loss in FAB-MS. Only FD-MS yielded the molecular ion as the base peak of the spectrum in all cases. Optimised FD emitter heating conditions allow the remaining portion of the thermally-induced CO loss to be significantly reduced.