Eighteen persons, dentists and nurses, with urinary mercury levels higher than the group median value of all dental personnel in the country of Västerbotten were compared with a group consisting of 15 persons with low urinary mercury levels working in the same clinics. A statistically significant difference between the high urinary mercury group and the low urinary mercury group could be seen in the plasma mercury level. In each group a statistically significant relation could be seen between the plasma mercury level and the total number of amalgam surfaces. The two groups did not differ with regard to the levels of plasma selenium and erythrocyte glutathione peroxidase, and no correlation between these two variables and the plasma mercury levels could be found. To evaluate organ functions, a large number of supplementary analyses were performed. These analyses did not indicate any influence on organ functions. Although the persons in the present study were occupationally exposed to mercury, none of the biologic variables analyzed seemed to be affected. Even among dental personnel who handle amalgam professionally the number of amalgam surfaces is a major contributory factor to the P-mercury level.