Idiosyncrasy: Specific (and usually unexplained) reaction of an individual to e.g. a chemical exposure to which most other individuals do not react at all. General allergic reactions do not fall into this category.
In silico: a term used to describe a computerised analysis of the structure of a chemical to assess its potential hazard.
In situ hybridisation (ISH): Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells.
In vitro: A Latin term used to describe effects in biological material outside the living animal (literally 'in glass').
In vivo: A Latin term used to describe effects in living animals (literally 'in life').
Incidence: Number of new cases of illness occurring during a given period in a specific population.
(Enzyme) Inducing agent: A chemical which, when administered to an animal, causes an increase in the expression of a particular enzyme. For example, chlorinated dibenzodioxins are inducing agents which act via the Ah-receptor (qv) to induce cytochrome P450 (qv) CYP1A1.
Intraperitoneal: Within the abdominal cavity.
Isomer: Isomers are two or more chemical compounds with the same molecular formula but having different properties owing to a different arrangement of atoms within the molecule. The ß-isomer of alitame is formed when the compound degrades and the atoms within the molecule are rearranged.