The gas-phase reactions of lanthanide (Ln + =La + -Lu + , except Pm + ) and actinide (An + =Th + , U + ) cations with iron pentacarbonyl, Fe(CO) 5 , and with ferrocene, Fe(C 5 H 5 ) 2 , were studied by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). In the case of Fe(CO) 5 , the observed primary products were of the type MFe(CO) x + (M=La, Ce, Pr, Nd, Gd, Tb: x=3; M=Ho, Er, Lu: x=3 and 4; M=Sm, Eu, Dy, Tm, Yb: x=4; M=Th, U: x=2 and 3) and evidence was obtained for the presence of direct Ln Fe and An Fe bonds in these species. With Fe(C 5 H 5 ) 2 the An + cations and the majority of the Ln + cations reacted by metal exchange, yielding Ln and An biscyclopentadienyl ions M(C 5 H 5 ) 2 + , while the less reactive Ln + cations formed the 'adduct' ions LnFe(C 5 H 5 ) 2 + . The product ion distributions observed with the two organometallic reagents and the reaction efficiencies obtained in kinetics studies both revealed a close relation with the relative stability of the accessible formal oxidation states of the metal cations. A few thermochemical estimates pertaining to the different species formed in the reactions could also be made. Reactivity studies of Ln, Th and U oxide and hydroxide cations with the iron complexes are also reported.