This study shows that individuals with dental amalgam fillings who exhibit symptoms typical of chronic mercury poisoning, all have mercury vapour concentrations in their oral cavity far higher than acceptable levels and on average, higher than the maximum permitted levels for the industrial environment. Results indicate that those patients with only amalgam fillings, high concentrations of mercury vapour in the oral cavity, and who have also many amalgam surfaces, exhibit on average more symptoms than those with lower concentrations of mercury vapour and few amalgam surfaces. The results indicate that the presence of symptoms is not solely dependent on the size of mercury dose.