Lead and mercury are naturally occurring elements in the earth's crust and are common environmental contaminants. Because people concerned about possible exposures to these elements often seek advice from their physicians, clinicians need to be aware of the signs and symptoms of lead and mercury poisoning, how to investigate a possible exposure and when intervention is necessary. We describe 3 cases of patients who presented to an occupational medicine specialist with concerns of heavy metal toxicity. We use these cases to illustrate some of the issues surrounding the investigation of possible lead and mercury exposures. We review the common sources of exposure, the signs and symptoms of lead and mercury poisoning and the appropriate use of chelation therapy. There is a need for a clear and consistent guide to help clinicians interpret laboratory investigations. We offer such a guide, with information about population norms, lead and mercury levels that suggest exposure beyond that seen in the general population and levels that warrant referral for advice about clinical management.