We will present here work done on identification of protein modifications induced by cigarette smoke, particularly protein oxidation and nitration, using on-line nanoLC, ECD hyphenation on a FT-ICR instrument (Fourier Transform - Ion Cyclotron Resonance). Briefly proteins were separated on a nanoLC column packed with C4 wide bore phase, then analyzed on FT-ICR mass spectrometer. Intact proteins were fragmented using ECD (Electron Capture Dissociation). This set-up is very efficient as the analysis can be performed on 10 picomoles of proteins allowing us to work on human plasma. Model proteins (cytochrome C and a-lactalbumine) were firstly oxidized using hydroxyl and nitroxyl radicals generated in solution. Hydroxyl radicals were produced by various Fenton reagents (Cu+ or Fe2+ and hydrogen peroxide) whereas nitroxyl radicals were generated by 3-morpholinosydnonimine salt. The mass accuracy obtained using the FT-ICR device coupled to ECD fragmentation, which is better than the 0.1 mass unit for a protein of a molecular weight of 10,000 Da, showed that methionines were oxidized to sulfoxides and peptide backbone fragmentation occurred. For example ß-scissions were observed as indicated by a loss of acetone from valine and leucine residues. The oxidation was further studied on "peptide scale" using a preliminary protein digestion. The generated peptide mixture was analyzed using separation on a C18 nanocolumn and FT-ICR MS/MS. Nitrosation was similarly studied. In a second step, cigarette smoke produced by a smoking machine was bubbled with or without a Cambridge filter on the same model proteins. The protein modifications will be compared to those obtained by model reactions described above. The study of proteins from human plasma treated with cigarette smoke condensate is currently under investigation.