Abstract
The rat liver microsomal enzyme system which is responsible for the metabolism of many foreign compounds has been shown to be affected by the ingestion or injection of a variety of chemicals. m-Terphenyl stimulates enzyme activity, whereas structurally related compounds do not. Caffeine may stimulate or inhibit, depending on the dose and length of treatment. Mercury compounds, both organic and inorganic, inhibit liver microsomal enzyme activity. Since many compounds appear to affect this enzyme system, one should be aware of the potential that exists for joint action among compounds that inhibit or stimulate microsomal enzyme activity, and those that are metabolized by this enzyme system to products that are more or less toxic than the parent compound.