Urinary levels of mercury (HgU) were measured in 93 males and females aged 18-63 years. Subjects with amalgam fillings (n = 72) had, on average, significantly higher levels of mercury in urine (mean = 0.57 microgram Hg/l and 0.79 microgram Hg/g creatinine, respectively) than subjects without amalgam fillings (n = 21; mean = 0.18 micrograms Hg/l and 0.24 microgram Hg/g creatinine, respectively). Urinary mercury excretion was significantly correlated with the number of amalgam surfaces (log HgU (microgram/l) vs. number of amalgam fillings: r = 0.435, P less than 0.001; log HgU (microgram/g creatinine) vs. number of amalgam fillings: r = 0.575, p less than 0.001). The results indicate that internal mercury exposure from amalgam fillings is, on average, higher than internal exposure to mercury from food and other sources.