catalysed by isoenzymes of cytochrome P-450, the terminal oxidase of the microsomal mono-oxygenase system. The activation of the halogenated compounds, which is a prerequisite for their hepatotoxicity, takes place at the haem moiety of these cytochromes, the site where normally 0, becomes activated during the mono-oxygenase cycle. Because of the common activation site, there is a competition be...