Acrylamide (AA) is a carcinogen in experimental animals. Glycidamide (GA), formed by metabolic epoxidation of AA, is believed to be responsible for the carcinogenicity of AA. Occupational exposure to AA has been assessed earlier by measurement of its adducts with N-terminal valine in hemoglobin. A background of AA adducts [N-(2-carbamoylethyl)valine (AAVal), about 30 pmol/g globin] was found in individuals without known exposure to the compound. The method previously available for adducts of GA only allowed analysis of samples from highly exposed individuals and showed similar levels of AAVal and adducts of GA [N-(2-hydroxy-2-carbamoylethyl)valine (GAVal)]. We have developed a sensitive method for simultaneous quantification of adducts of GA and AA, which is suitable down to low exposure levels. The method is based on the so-called modified Edman method, where globin is reacted with pentafluorophenyl isothiocyanate under neutral conditions. The valine adducts are then extracted in the form of pentafluorophenylthiohydantoin (PFPTH) derivatives. The analytical procedure included reaction of the PFPTH derivatives with acetic anhydride in order to protect the hydroxyl group of GAVal. The PFPTH derivatives of AAVal and GAVal were analyzed by gas chromatography/tandem mass spectrometry. ( 2 H 3 )AAVal-PFPTH was used as the in-ternal standard. The method was applied to samples from 11 workers at an AA production plant, 1 nonexposed nonsmoker, and a few participants of a smoking cessation program. AAVal levels were in the range 27-1854 pmol/g globin. Recorded levels of GAVal were 3-12% of those of AAVal, suggesting that previous measurements of GAVal overestimate GAVal at low levels of exposure to AA.