Abstract
A study has been made of the use of 24-hour excretion (actual or projected) in comparison with the concentrations adjusted for specific gravity, as measures of exposure to lead, mercury, benzene, and trichloroethylene. It has been found that timed samples show a somewhat greater variation than values adjusted for specific gravity. When different individuals are considered, differences in body size affect the rate of excretion, as indicated by timed samples, to a certain extent. Other factors, however, appear to be of greater importance. The evidence presented, although not conclusive, suggests that the value adjusted for specific gravity is a better index of exposure than is the timed sample.