Electrospray mass spectra derived from dichloromethane or dichloromethane/methanol solutions of cationic and anionic metal carbonyl compounds are reported for the first time. The cations investigated are the seven coordinate species [M(CO)2(PP)2 X]+ (M Mo, W; PP diphosphine or similar ligand; X F, Cl, Br, I) and carbonyl phosphonium or arsonium cations of the types [M(CO)3(η-PPMe)(η2-PP)], (M Cr, Mo, W), [M′(CO)2(η2-PPMe)(η2PP)X]+ (M′ Mn, Re). These cations were prepared by the action of Mel on M(CO)3(η1PP)(η2-PP) and [M′(CO)2(η1PP)(η2PP)X, respectively, each of which contains a pendant Group 15 atom. The anionic species investigated are [M(CO)5X]- and [M′(CO)4X2]-. In all cases the dominant peak in the mass spectrum corresponds to the principal ion known to be present in solution.