The realization that certain occupations were hazardous to the worker’s health by virtue of exposure to chemicals in the workplace had its origins more than 200 years ago. In 1775, Percival Pott, a surgeon at St. Bartholomew’s Hospital in London, England, identified the first occupational carcinogen by attributing the high incidence of scrotal cancer in chimney sweepers to their occupational exposure to soot. The balance between metabolic activation and inactivation reactions, as well as the inherent carcinogenic activity of the ultimate electrophilic metabolite, are undoubtedly important factors in determining the potency of a chemical carcinogen. Enzymes involved in the initial stages of metabolism of chemical carcinogens act to convert foreign, lipophilic compounds into more hydrophilic forms that can be readily excreted. Conjugation reactions are particularly important for deactivation of carcinogens, but in some cases can lead to bioactivation.