Fast atom bombardment (FAB) mass spectrometry of the two hydrido carbene compounds trans-[(PPh3)2HPt(carbene)]BF4 (carbene = CSCH2CH2S and COCH2CH2O was studied. Some retrosynthetic processes are involved in the fragmentation pathways. The reactions with NaCl were also studied under FAB conditions and the results were compared with those obtained in solution.