ABSTRACT
The relationship between the dose of a compound and its toxicity is central in toxicology. Paracelsus (1493-1541), who was the first to put toxicology on a scientific basis, clearly recognized this relationship. His well-known statement: “All substances are poisons; there is none that is not a poison. The right dose differentiates a poison and a remedy” has immortalized the concept. Implicit in this statement is the premise that there is a dose of a compound, which has no observable effect and another, higher dose, which causes the maximal response. The doseresponse relationship involves quantifying the toxic effect or response and showing a correlation with exposure. The relationship underlies the whole of toxicology, and an understanding of it is crucial. Parameters gained from it have various uses in both investigational and regulatory toxicology. It should be appreciated, however, that toxicity is a relative phenomenon and that the ways of measuring it are many and various.
