Selenium may have a protective effect against mercury toxicity. The aim of the present study was to investigate if selenium excretion in urine was affected in persons with dental amalgam fillings. The reason for this study is that dental amalgam is the most important source of inorganic mercury exposure in the general population, although the potential toxic effects of this exposure remain a subject for debate. The chelating agent 2,3 dimercaptopropane-1-sulfonate (DMPS) was injected intravenously (2 mg/kg) to provoke metal excretion. Urine samples were subsequently collected at intervals over a 24-h period. Selenium concentration was determined by hydride-generation atomic absorption spectrometry. The study was comprised of 20 persons who claimed symptoms from dental amalgam and 21 healthy persons with amalgam fillings. There were two control groups without amalgam. One control group had amalgam replaced because of concern about illness resulting from mercury release (n = 20), whereas the other control group never had amalgam (n = 19). Individuals with amalgam excreted less selenium (36.4 microg, median value) over 24 hours than those without amalgam (47.5 microg) (p = 0.016). There was no difference in selenium excretion between groups with (42.4 microg) and without (39.4 microg) amalgam-related symptoms (p = 0.15). The findings indicate that individuals exposed to low levels of elemental mercury from dental amalgam excrete less selenium to urine than unexposed individuals.