 Trevans concept of median lethal dose, MLD, has been widely used in toxicology studies since it was introduced in 1927. However, animal ethicists have criticized the use of LD50 tests due to their irreproducibility and lack of information regarding the full spectrum of toxicity. Recent research has focused on developing alternative methods such as Finney's probit analysis and the Litchfield and Wilcoxon method which can be used to determine the best estimate of LD50. These methods provide more accurate results and allow for a better understanding of the dose response relationship between a substance and its effects on living organisms. This article was authored by Sadasivan-Califl-Palai, Katsumi Kobayashi, Matthews Michael, and others.