LD50 - Lethal Dose 50%

This Note is designed to provide guidance to RSC members and may also be useful to others with a particular interest in the subject.

The LD50 test and its variants are now considered obsolete. Internationally accepted alternative tests, using fewer animals and "absence of evident toxicity", rather than death, as their criterion, have been developed. They are accepted by most regulators as valid alternatives to LD50 testing which, previously, was usually undertaken as a result of then legislative requirements.

Nonetheless, LD50 values are still quoted and enquiries received by the Royal Society of Chemistry suggest that there is still a need for information about their meaning. This note aims to provide basic information about LD50. Readers are urged to obtain more detailed information, if required.