Elemental mercury (Hg degrees) in urine samples from workers in thermometer manufacturing factories was determined. In a factory in which the mercury level in the ambient air averaged more than 0.1 mg Hg m-3, the Hg degree concentration in the workers' urine ranged between 0.05 and 1.7 micrograms Hg 1(-1) and constituted less than 1% of the inorganic mercury (In-Hg) in urine. Higher amounts of Hg degrees could be detected in urine on the day of the filling operation when thermometer blanks were filled with metallic mercury and on the following day when compared with other days. During this operation, the workers were exposed to mercury vapor levels with as much as 0.47-0.67 mg Hg m-3. Our findings suggest that Hg degrees appears in urine quite rapidly after the worker's exposure to unusually high mercury levels.