The covalent binding of chemical carcinogens and mutagens to hemoglobin has been proposed as a dose monitor for environmental exposure. The binding of chloroform and bromoform to hemoglobin in rats was demonstrated to result from the formation of adducts to amino acids in the globin. The altered amino acids were isolated with an amino acid analyzer employing ion exchange chromatography. At low doses the covalent binding of chloroform, and 2-acetylaminofluorene, were linearly related to dose. At higher doses, the binding increased as a non-linear and decreased function of dose. A pharmacokinetic model was described that relates the dose as determined by hemoglobin binding, to exposure, and carcinogenic potency. The quantitative difference of carcinogenic potencies for chemical carcinogens was not reflected to the Hemoglobin Binding Indices of the carcinogens. Therefore, the binding of a carcinogen to hemoglobin appears to be suitable for use in the estimation of the systemic dose and exposure to the carcinogen but not for the estimation of the carcinogenic potency.