Nine healthy volunteers without amalgam fillings were exposed to 400 micrograms/m3 mercury vapor (Hg0) for 15 min, corresponding to 5.5 nmol Hg0/kg body wt (median range: 4.4-7.2). Frequent sampling of blood, urine, and exhaled air was performed for 30 days after exposure. The median retention of Hg0 was 69% of the inhaled dose. During the first 3 days after exposure 7.5-12% of the absorbed dose was lost by exhalation, with the median half time of Hg0 in expired breath being 2.0 days. In blood and plasma, a rapid absorption phase of Hg was seen, followed by a biexponential decline of the curves in both media. A substantial interindividual variation was observed in the area under the concentration-time curves of Hg in blood and plasma. In plasma the median half time of the second phase was 10 days. About 1.0% of the absorbed Hg was excreted via urine during the first 3 days after exposure, whereas the estimated amount excreted during 30 days ranged from 8 to 40%. In order to evaluate the chronic exposure to mercury from dental amalgam in the general population, the daily Hg dose from the fillings were estimated based on the plasma Hg levels found in subjects with amalgam fillings and on the plasma Hg clearance obtained in the present study. The daily Hg dose was estimated to 5-9 micrograms/day in subjects with an ordinary number of amalgam fillings.