Within 9 days after removal of the fillings, a transient increase was observed in plasma Hg levels only. This was reduced in those volunteers to whom a rubber dam had been applied during removal. Peak plasma Hg was 0.6 ng/ml on average and decreased with halftimes between 5 and 13 days. A significant decrease in Hg excretion was noted not before 100 days after removal. Being relatively insensitive to dietary mercury, the determination of total mercury in plasma and of its urinary excretion rate appears, under practical aspects, most suitable for the investigation of Hg uptake from amalgam.