The present study reports a procedure developed for the identification and quantitative analysis of the adducts formed by interaction of methyl bromide with human hemoglobin, based on combined analysis by electrospray mass spectrometry and automated Edman degradation of either intact globin chains or tryptic peptides of globin chains. The procedure has allowed identification of the reactive sites in human hemoglobin, and has been applied to the analysis of samples modified in vitro by methyl bromide. The results obtained represent the basis for the complete structural characterization of the modified hemoglobin and demonstrate the usefulness of the proposed analytical approach for the evaluation of the degree of alkylation and the identification of modified amino acids in proteins.