The levels of elemental and inorganic mercury were measured in urine and blood samples from workers in thermometer manufacturing factories. The inorganic mercury levels in the urine did not correlate with the levels of mercury exposure for each worker. However, a significant correlation was noted between elemental mercury levels in the urine and the levels of individual exposure. A significant correlation was also found between elemental mercury levels in the urine and mercury levels in the blood. These findings suggest that the determination of elemental mercury in urine may serve as a useful indicator for assessing levels of recent exposure to mercury vapor, as well as the level of inorganic mercury in the blood.