Three healthy volunteers were exposed to 1, 4-dichlorobenzene (p-DCB) vapor (2.4-2.8 ppm) for 1 hr, peripheral blood was taken before and after exposure. Serum was collected and incubated with calf thymus DNA to examine whether there are any DNA-binding metabolites persisting in human serum. Among the 3 subjects we detected 4, 2, and 0 DNA adducts respectively, no differences were found in adduct profiles before or after p-DCB inhalation. The result reflects that qualities and quantities of DNA-reactive metabolites in human sera are different, depending upon individual exposure to environmental carcinogens and their metabolism ability. There were no additional DNA-reactive metabolites found after inhalation exposure to p-DCB.