The article by Thomas W. Clarkson reviews the three modern faces of mercury: methyl mercury in fish, mercury vapor from amalgam tooth fillings, and ethyl mercury in the form of thimerosal in vaccines. It discusses the mechanisms of action, human exposure, disposition in the body, and adverse effects of each form of mercury. Key gaps in current knowledge are identified, particularly regarding the toxicology of ethyl mercury and its comparison to methyl mercury. The review highlights the public health concerns and regulatory actions related to these forms of mercury, emphasizing the need for further research to understand their health risks.The article by Thomas W. Clarkson reviews the three modern faces of mercury: methyl mercury in fish, mercury vapor from amalgam tooth fillings, and ethyl mercury in the form of thimerosal in vaccines. It discusses the mechanisms of action, human exposure, disposition in the body, and adverse effects of each form of mercury. Key gaps in current knowledge are identified, particularly regarding the toxicology of ethyl mercury and its comparison to methyl mercury. The review highlights the public health concerns and regulatory actions related to these forms of mercury, emphasizing the need for further research to understand their health risks.