The mass spectra of a number of simple monomeric manganese carbonyl complexes of formula LMn(CO)5 have been investigated in order to look for general features in their fragmentation patterns. The observed metal-containing ions are derived from the molecular ion by four types of fragmentation process: (i) the commonly observed stepwise loss of carbonyl groups; (ii) loss of the ligand L; (iii) loss of ligand fragments from atoms attached to the metal atom; (iv) rearrangement involving transfer of fragments to the metal atom, with elimination of the remainder of the ligand. Some investigations on the mechanism of these rearrangements have been carried out.