The development of procedures for retrospective detection and quantitation of exposure to phosgene, based on adducts to hemoglobin and albumin, is described. Upon incubation of human blood with [14C]phosgene (0-750 μM), a significant part of radioactivity (0-13%) became associated with globin and albumin. Upon Pronase digestion of globin, one of the adducts was identified as the pentapeptide O=C-(V-L)-S-P-A, representing amino acid residues 1-5 of α-globin, with a hydantoin function between N-terminal valine and leucine. Micro-LC/tandem MS analyses of tryptic as well as V8 protease digests identified one of the adducts to albumin as a urea resulting from intramolecular bridging of lysine residues 195 and 199. The adducted tryptic fragment could be sensitively analyzed by means of micro-LC/tandem MS with multiple-reaction monitoring (MRM), enabling the detection in human blood of an in vitro exposure level of ≥ 1 μM phosgene.